Computer Hardware Troubleshooting Notes

Hardware Troubleshooting Notes

Power problems or no power

  1. Check power outlet or power plug.
  2. Check power cable by checking it with multimeter or interchange with monitor cable.
  3. Check SMPS  switch that it is off or not.
  4. Check all SMPS  connections that they are inserted correctly or not or remove not relevant links.
  5. If the system starts for some time and then off then check CPU   heat sink and fan are inserted properly, removing power connector from Hard disk, Floppy drive, CDRAM, check Motherboard capacitors.
  6. Check front panel connectors such as power button are inserted correctly on the Motherboard or not.
  7. Check RAM  by inserting another RAM.
  8. Check SMPS  by replacing it with another working SMPS.
  9. Check CMOS battery or insert another battery.
  10. Check Motherboard.

Display problems

  1. First of all, check that whether monitor or CPU  is faulty by starting the system and click on num lock key. If it is on and off continuously by clicking then a problem is in monitor data cable, Display card, Monitor color settings, CMOS battery weak or dust in RAM. If it is not changing than the problem is in CPU.
  2. For the problem in CPU  first of all check RAM  by removing dust from RAM, insert into another slot or replace with another working RAM  or cleaning the RAM  slots from isopropyl, thinner or petrol.
  3. Check CMOS battery voltage (3.35v dc), clear the CMOS settings or replace with another CMOS battery.
  4. Check SMPS  by replacing with another working SMPS.
  5. Check all the SMPS  connections, cables connections, check whether all cards are inserted correctly in slots or remove all unnecessary connections leaving only SMPS  connections and then attach all cards and cables one by one.
  6. Eliminate the motherboard from the cabinet and then check display by attaching only SMPS , motherboard, CPU  , RAM , keyboard and power cable outside and starts the system by shorting the power button on m/b by Screwdriver. if display comes then check it for 5-6 times and then inserted into cabinet before checking that anything in cabinet is shorting the m/b or keep the foam sheet or paper on cabinet.
  7. Check CPU   by replacing with another working and compatible CPU   or refreshing the CPU   by removing CPU, RAM, CMOS battery from m/b and the on the system for 10-15 minutes, then attach all these and then starts the system.
  8. Shorting all the capacitors on m/b from a Screwdriver.
  9. Replacing the BIOS chip which is compatible or same.
  10. Check the motherboard.


Hanging problems

  1. First of all check CPU   fan and heat sink that whether they are connected properly.
  2. Check RAM  by inserting into another slot.
  3. Check SMPS  that whether they are not providing required voltages.
  4. Remove all unnecessary cards and then check that may be any card is faulty .also replace the Hard disk cables.
  5. records check operating system that any file is corrupted or not, any software that creating problems by removing the unnecessary software, delete all temporary files and files that are not needed, defragmenting the hard disk or removing icons from the startup by typing msconfig at run and then click on startup and uncheck all unnecessary applications or start the system in safe mode and then remove all the drivers and then restarts the system.
  6. Check for viruses.
  7. Format the partition and reinstall the operating system.
  8. Check Hard Disk for bad sectors.
  9. If the system hangs after inserting the CDRAM   or floppy disk then check whether CDRAM   or floppy disk is faulty or CD drive and floppy drive has a problem.
  10. Check Motherboard capacitors.


Hard disk problems

  1. If a hard disk is not detected then check Hard disk cables, attach Hard disk cable on different hard disk ports, check master-slave condition or attach one device to one cable. Interchange hard disk and CD-ROM cables.
  2. Go to CMOS setup screen and then detect theHard disk manually by clicking on hard disk auto detection or go to standard CMOS setup screen and click

Enter on all four options such as primary master, secondary master, etc.

  1. Make the drive master if it is the slave.
  2. Check power connector by attaching another power connector or check logic card by connecting another compatible working logic card.
  3. If MBR is corrupt or we can’t create any partitions then give the command “a:\>fdisk /MBR” to repair the MBR or restore the MBR from utility software.
  4. Check hard disk for bad sectors by slow formatting the partition or with part utility software and then block the bad sectors.
  5. if an operating system is not installed then check the hard disk for bad sectors, check whether the partition is active and primary or not, or whether partition file system is compatible with o/s or not. Then test the RAM .
  6. If “tic tic tic “sound comes from hard disk, then hard disk media has a problem.


CDRAM  /cd-writer/combo/DVD-writer problems

  1. If CDRAM   is not detected then check cables, ports, master-slave condition, manually detect in CMOS setup, check logic card, and check power connectors.
  2. If the cd is not read then clean the lens from cotton, lens cleaner cd or change the cd, drive head lens with another compatible lens head.
  3. If a tray is not in and out properly then clean the cd drive dust, tray corners with grease, change tray belt.
  4. If the picture is not clear or image is running very slow then increase the cd rays by adjusting the small screw near the cd lens.
  5. If a cd is not written but read in cd-writer, then uninstall and reinstall the compatible cd writing software such as lG Nero with LG cd writer.
  6. If DVD video disk is not played in DVD drive, then install the DVD playing software such as power DVD, Win DVD.
  7. If the video is not clear, then install the latest DirectX software such as DirectX 9.0c.


Sound related problems
If there is no sound then check speaker is on, speaker volume is high, lead is connected to the proper port on a PC, and volume is not low from volume properties and from software on a PC.

  1. Check from device manager that sound driver is correctly installed or remove and reinstall the proper driver.
  2. Data cable of Sound card may be connected the wrong side.
  3. Remove and reinstall the sound playing software.
  4. Insert the sound card in another slot and remove the driver from safe mode and reinstall the proper driver.
  5. Check whether an onboard sound is disabled from the CMOS settings or m/b with the help of jumpers.
  6. If we use a sound card and there is also onboard sound then disabled the onboard sound from CMOS for proper working.
  7. Format and reinstall the operating system and then install the actual driver.
  8. If sound not comes in audio cd but comes in mp3 songs, then attach the audio cable on m/b with CDRAM.
  9. Insert another working sound card and then install its drivers.
  10. If the music comes from 2-3 days but not now, then in Win XP, 2003 restore the system to an earlier state with system restore utility.


Mouse problems

  1. If serial mouse is not detected then remove its driver from device manager in safe mode and restart the system otherwise delete the lmouse.vxd key entry from registry. Check mouse on other system. If port is not onboard then check its cable connections on m/b that they are connected wrong side or change the wire. If it is 1 by 1 wire, attach 4 by 5 cable or vice-versa. Check if serial port is disabled from the CMOS setup. If ps2 mouse is not detected then remove and reinstall its driver, check if ps2 port is not disabled from the CMOS, check ps2 port cable connection or replace the wire. if USB mouse is not detected then install its driver in win98, interchange USB ports, check if USB port is not disabled from the CMOS otherwise test the USB port cable connection .if all these not works then check the pins on mouse cable or attach another compatible cable.
  2. If mouse not rotates correctly, then clean the dust from cotton buds in rollers.
  3. If the wireless mouse is not detected then check sensor connections battery and reinstall the drivers.


Keyboard problems
If k/b is not detected then check its connections, check converter if attached, replace the cable with same compatible cable. Also check onboard k/b controller by inserting k/b in another system. If USB k/b is not detected then check whether USB k/b legacy support is disabled from the CMOS and also check its drivers from device manager. If some keys are not working properly then remove the dust from keys or open the k/b and clean the keys or replace with other working key. In mechanical k/b desolder the wrong key and soldered the other working key. If wireless k/b is not detected then check the sensor connections battery or uninstall and reinstall the drivers again.


Modem problems

If internet is not connected then check modem settings such as diagnose the modem, uncheck wait for dial tone before dialing, check tone or pulse dial, check dialing properties, remove & recreate the dial up connection again, check whether username or password and phone no. is correct check phone line connected to the modem port, check modem by giving mobile phone no. in dial-up connection and then click on join. Otherwise, remove the drivers from safe mode and reinstall the drivers & make its settings again. Otherwise, attach the modem in the different slot. Check whether username and password are correct by giving BSNL or SIFY registration username & password to check. Also, check whether phone line has the dial tone or not by attach the line to the phone and check dial tone.

If mobile phone modem is not connecting then uninstall and reinstall its driver and software, check cable, check username & password, check cell phone settings such as baud rate, check whether internet service is active from a phone. Also, check serial and USB ports where the cable is connected such as com1 in serial cable or whether ports are disabled from the CMOS. Otherwise call the call center.
If broadband internet connection has a problem, then check all its cable connections, check username & password, recreate dial-up connection, check whether phone line has some disturbance.

LAN problems
Remove and reinstall the driver again, check IP address subnet mask, workgroup name, services & protocols, log on to the computer from computer network name, check the cable connectors or cables. Otherwise, change the card slot and reinstall the driver after removing old drivers from safe mode.

SCSI problems

Check for proper termination, check SCSI id, check for compatible signaling variations such as LVD, HVD, so. Install the card drivers and device drivers, check settings from SCSI CMOS setup, check cable connectors.

Floppy drive problems
If the floppy disk is not read or not work properly the format the floppy disk or insert another working floppy disk, check writes protect notch if we can’t write anything on the floppy. If floppy drive light glows continuously attach the cable from reverse side or change the wire. Check whether the floppy drive is disabled from CMOS if it is not detected. Clean the dust from a floppy drive or aligning its head properly if no floppy reads in the floppy disk. Disabled swap floppy drive and floppy drive seek from CMOS if the floppy drive is not detected.


Memory problems

  1. If the system gives long continuous beep on starting the system, then check for RAM.
  2. If the blue screen or fatal error is displayed on screen then first format the partition and install the o/s else clean the RAM  slots or change the RAM  .this also applies if windows protection error is displayed on the screen.
  3. If o/s is not installed correctly and it gives unknown errors while installing then change the RAM.


CMOS password breaks or default the CMOS settings methods


  1. Remove the battery, power cable from SMPS  & then on the system without battery after 4-5 minutes. Then insert and save the settings after settings come to default.
  2. Short the clear CMOS pins on m/b from jumpers or screwdriver after turn off the system.
  3. Press “f and j” key together and then activate the system to make default the CMOS settings.
  4. Remove the setup password from CMOS software.
  5. Remove the installation password from debug command in win98:-

-o 70 2e
-o 71 ff
-o q

Installation of drivers

  1. run setup if onboard
  2. install from device manager if in a card form
  3. For installing any USB device first install the driver or software & then connect the device to the system.
  4. Add parallel printers and the external modem (56kbps) from a control panel.

Post messages

  1. 1xx = system m/b failure
    2. 101 = interrupt failure
    3. 103 = timer interrupt failure
    4. 109 = dma test error
    5. 161 = CMOS battery fail
    6. 164 = memory size error(run CMOS setup & configure the memory bus speed & memory size)
    7. 2xx = (any number starts with two). Problem with memory. One or more partition of RAM  is bad.
    8. 201 = memory test failed. One or more partition of RAM  is bad.
    9. 3xx = this is the problem of keyboard.
    10. 301 = keyboard error (any key is pressed during the post on booting). You will see any error message or any beep continuously.
    11. 4xx = this is a problem of monochrome display problem
    12. 5xx = color video problem.
    13. 6xx = floppy disk system problem.
    14. 601 = floppy disk error (floppy adapter or floppy drive failed).
    15. 17xx = hard disk problem (the hard disk information may not be set correctly or the disk adapter can’t communicate with the HDD).
    16. 1780 = IDE one drive failure or primary drive failure. (IDE one drive controller is not functioning). The hard disk is not configured properly or the controller is not installed correctly

post audio messages

  1. No beep or nothing happen – power supply bad or not connected.
    2. Continuous beep:- power supply bad or any key of keyboard pressed.
    3. One long & one short beep: – system board failure.
    4. One long beep & two short beeps: – display card not connected or loose or failed.
    5. One short beep with the blank screen: – display card problem. Display card not set properly or damage.
    6. One short beep with no beep: – floppy drive adapter is the failure.
    7. Two short beeps:- ps2 configuration errors
    8. Long beep continuously: – RAM  problem. RAM  is faulty. RAM  is failed or loose.



  1. partition made but no partition gets detected:-

(i). Maybe partition hides.
(ii) Partition creates through dos bootable floppy but system boot with win 98 floppy.
(iii) Partition creates with win98 bootable floppy but boots with dos bootable floppy.
(iv) Logical partition NTFS or non-dos or hpfs and CDFs.

  1. wrong display driver loaded :-

(i) Windows protection error.
(ii) Windows corrupt.
(iii) System does not booting in normal mode.

  1. while loading DOS message shows(incorrect dos version):-

(i Maybebe partition formatted through windows bootable.
(ii) Partition created through windows and also formatted with windows.
(iii) System boot from dos and command run from windows.

  1. while installing windows system hangs:-

(i) cd is damaged or corrupt.
(ii) RAM  problem.
(iii) Bad sectors on the hard disk.
(iv) Partition problems.
(v) CPU   fan problem or CPU   heated.

  1. system hangs after c:\> prompt:-

(i) RAM  problem.
(ii) MBR is corrupt.
(iii) FAT problem.
(iv) Bad sectors on the hard disk.
(v) Virus in the system.
(vi)Boot record is modified or corrupted.

  1. system working after one hour give the beep:-

(i) CPU   overheated.
(ii) Motherboard heat up or motherboard damage.

  1. CMOS setup automatic open as soon as system on:-

(i) Set the speed of CPU  to go to the CMOS installation.
(ii) May be DEL key is pressed while booting.

  1. HARD DISK protection error:-

(i) In the CMOS setup, hard disk protection error is enabled.

  1. error reading fixed disk drive (error shows after FDISK):-

(i) May be data cable is not connected properly or replace the data cable.
(ii) MBR problem or MBR is corrupt
(iii) Run at prompt a:\>fdisk /MBR.
(iv)Run disk manager and use the zero fill formatting to remove the problem.

  1. I/O error(error shows):-

Reason: (i) IO.SYS file corrupt or missing.
(ii) CONFIG.SYS corrupt or missing.
Solution: (i) transfer the system files.
A:\. SYS C:

11No room present or available (message shows):-
(i) The system moved by dos but partition made by windows.

12. Partition made but system is not booting:-
(i) Partition is not active.
(ii) Booting files are corrupted.
(iii) In CMOS first boot device set to CDRAM   and others are disabled.
(iv) The operating system is corrupt.

13. Fat16 partition is made from windows but the system transferred from dos & system does not boot:-
Reason:- (i) cluster size changed for dos.
(ii) Boot record is changed.
Solution: – (i) create the partition through dos and transferred the system files.

14. Primary hard disk fail or secondary hard disk fails (message shows):- 
(i) Check the data cable.
(ii) Check the jumper setting.
(iii) Check the power supply connector.
(iv) Check the CMOS setting.

15. a sector not found:-
(I) Use any utility to recovering the files.
(ii) Use SCANDISK as utility.
(iii) Use “low level format through dm”.

16. no fixed disk present(message shows):-
(i) Connect the power supply connector correctly.
(ii) If data cable damaged then use another cable.
(iii) Use the auto detect option in CMOS to detect the HDD.
(iv) Check the logic card of hard disk.
(v) Check the different ports of m/b that these may be disabled in CMOS.

17. drive was formatted accidentally:- 
(i) Use an unformatted utility.
(ii) Use the data recovery third party utility for recover data.

18. drive is active but computer is not booting from HDD:-
(i) Drive failure problem.
(ii) Boot sector failure.
(iii) MBR corrupt.
(iv) DOS or WINDOWS system files are corrupt.

19. data head error (message shows) (in this error hdd or fdd can’t read data):-
(i) Run the CHKDSK at C :\>; check file structure & bad sectors & HDD problems.
(ii) Using NDD or other HDD repair utilities to repair HDD & FDD.

20. hard disk configuration error(message shows):-
(i) Incorrect configuration setting in CMOS setup.
(ii) Detect the hard disk from the CMOS installation.
(iii) Use “low level format” & “zero fill format” to repair the HDD.

21. hard disk controller failure:-
(i) Check in the CMOS that the HDD controller option is enable or disable.
(ii) Check the hard disk that is spinning or not.

22. invalid drive specification(message shows):- 
(i) Reasons:-invalid drive selected.
(ii) Invalid media type reading drive abort, retry, fail.
(iii) The partition made but the selected partition not is formatted.
(iv) Solution:-Format the partition and select the drive.

23. command interpreter is missing(shows like c>):-
Reason:- COMMAND.COM file is missing or corrupt.
Solution:- transfer the system files or copy the COMMAND.COM with floppy to hdd.

24. floppy disk error or floppy disk fail (message shows):-
(i) In the CMOS there is wrong floppy setting.
(ii) Power connector or data cable is not connected or loose or reverse connected.
(iii) Data cable is faulty.
(iv) Floppy drive is faulty
(v) Floppy disk port is disabled in CMOS.

25. display comes but when loading the windows or desktop no display on screen:-
(i) Go to safe mode and go to display properties ->settings and set the colors to 16 and click on apply & restarts the system or remove the display driver from add/remove progRAM s or remove from device manager and restarts the system.

26. when loading win98 system hangs after when we click continue on first setup screen and the progress bar goes to 100%:-
(i) Remove floppy disk from floppy drive or disabled the floppy drive from CMOS setup.

27. if sound not comes from headphone:-
(i) Check headphone cable that it is connected at proper port in sound card.
(ii) Double click sound icon in taskbar near date and then click on options and click check on microphone/headphone and click apply.
(iii) Check headphone on another system.

28. if colors are not proper on monitor or magnetic field build up due to keep speakers or any magnetic media near monitor:-
(i) Click on menu options on monitor where color settings are adjust and click on degauss to remove the magnetic field.

29. File copying error after copying a few files with long filenames to the floppy disk.
Cause: – root directory fills up due to a use of multiple directory entries by each long filename.
Solution: – create a folder on the floppy disk and copy files with long filenames into the folder.

30. can’t access full capacity of hard disk over 8.4gb:-
Cause: – BIOS is out of date.
Solution: – upgrade flash BIOS.

31. can’t use drive capacity above 528 MB:-
Cause: – LBA mode not enabled in BIOS.
Solution: – enable LBA mode.

32. your 40 GB hard disk can’t be formatted by windows 2000 or windows XP as a single drive with fat32:-
Cause: – these versions can format up to 32 GB only but can read larger drives.
Solution: – Prepare drive with third party utility such as Partition Magic or use NTFS.

33. UDMA/66 or UDMA/100 drive runs at UDMA/33 on systems that support UDMA/66 or UDMA/100.
Cause: – incorrect cable might be used.
Solution: – use 80-wire UDMA cable in place of regular 40-wire IDE cable.

34. Can’t set drives as master or slave when 80-wire cable is used.
Cause: – 80-wire cable supports cable select, not master/slave.
Solution: – install drives at correct locations on cable and jumper both as cable select.

35. conflicts between com ports:-
Cause: – IRQ’s shared between COM1 and 3; between COM2 and 4.
Solution: – disable unused COM port or change IRQ if possible.

36. standard keys on keyboard work but not multimedia or internet keys:-
Cause: – the keyboard driver is not installed or is defective.
Solution: – install the latest driver for your keyboard.

37. internal modem hangs the system when trying to connect to the internet:-
Cause: – Modem might be set to the same IRQ as the serial port the mouse is attached to.
Solution: – disabled the unused com port on the system and set the modem to use that com port number.

38. system locks up after installing internal modem:-
Cause: – IRQ conflicts with other ports or devices.
Solution: – use device manager to find conflicts and resolve them or uninstall and reinstall the drivers from device manager.

39. computer can’t detect external modem:-
Cause: – wrong cable, port problems, or power problems.
Solution: – check cable, port setup and power.

40. IP address conflict error:-
Cause: – duplicate IP addresses on two or more machines.
Solution: is disable- open network properties & enter correct unique IP address for each system

41. If system shutdown message is not displayed on AT SMPS  system or system shutdown message appears on ATX SMPS  systems.
(I) go to CMOS setup screen and enable power management or ACPI suppis disabledor vice versa or enable use ATX SMPS  option in ATX systems.

42. RAM  test not detecting any problems and is finishing too quickly.
Cause: – L1 and L2 memory caches might be enabled.
Solution: – disable memory caches before testing memory.

43. can’t use USB keyboard and mouse outside of windows that is in dos:-
Cause: – USB legacy support is disabled in CMOS setup.
Solution: – enable USB legacy support.

44. garbage appears on your video screen for no apparent reason:-
Cause: – hardware resource conflict.
Solution: – use device manager to find conflicts and resolve them.

45. can’t use AGP card as primary video:-
cause: – PCI video is set as primary video.
Solution:- switch main video to AGP card from CMOS setup such as select initial display as AGP.

46. display is steady at lower resolutions but flickers at higher resolutions:-
Cause: – higher refresh rates are needed at higher resolutions to avoid flicker.
Solution: – adjust display properties to higher refresh rates if supported by the monitor.

47. virus warning message triggered when trying to upgrade Windows:-
Cause: – Virus alert feature enabled in CMOS setup.
Solution: – disable virus warning or boot sector write protect feature.
48. the system locks up frequently and sometimes reboots on its own:-
(I) Check SMPS  and also check for viruses or go to power options in control panel and select “always on” in power scheme and in all the other options select “never” or reinstall the operating system.

49. when we create partitions on a hard disk more than 60 GB FDISK and DM software not show its space properly:-
(i) for this in FDISK we give space in percentage example in 80 GB fdisk shows hard disk capacity as 10GB only and for creating first partition of 20 GB we give 25% space.
(ii) When we use DM then it shows 14GB hard disk capacity, we ignore these values and give space which we want example give 20000MB to create the first partition then it shows 60GB as extended partition.
(iii) Otherwise update the FDISK and DM software to show actual space.

50. when we attach two hard disks how should we find the partitions of both HDD:-
(i) in win98, from which HDD we boot the system takes the c: partition,d: partition goes to the other hard disk first primary partition,then all the remaining partitions of hard disk from which we boot shows and then all the partitions of the remaining hard disk example c:\ partition of booting hard disk, d: partition of second hard disk, e:\ , f:\ , g:\ partitions of booting hard disk & h:\, i:\, j:\, partitions of second hard disk. In win2000/xp/2003 the starting all partition shows from first hard disk from which we boot and all the remaining partitions of other hard disk example c:\ , d:\ , e:\ . f: , of first hard disk & g:\ , h:\ , i:\ , j:\ of other hard disk.


IRQ # Device
0 System timer
1 Keyboard
2 Cascade to IRQ9. Can’t be used.
3 Com ports 2 and 4
4 Com ports 1 and 3
5 Usually available. Sometimes LPT2. Most often used for sound cards.
6 Floppy drive
7 LPT1
8 Real time clock
9 Video display adapter
10 Available
11 Available. SCSI adapter will usually use this IRQ.
12 Available or PS2 mouse
13 Math coprocessor.
14 Primary IDE controller
15 Secondary IDE controller. If there is no secondary IDE controller on the board, or secondary IDE controller is disabled in CMOS, IRQ 15 is available

52.I/O addresses

I/O Ports 
LPT1 378H
LPT2 278H

Dot pitch is the space between pixels in millimeters.
The refresh rate is the number times display is redrawn every second.
53.Video modes:-
CGA 640 x 200
EGA 640 x 350
VGA 640 x 480
SVGA 1024 x 768

54. Cache:
– L1/L3 – Internal Cache
– L2 – External Cache

Type 1 3.3mm Memory
Type 2 5mm Modems, Network cards
Type 3 10.5mm Hard Disks

56. Power Supplies 
Yellow: +12
Blue: -12
Red: +5
White: -5
Voltage for motor: +/- 12 volts
Voltage for circuitry: +/- 5 volts

57Repair corrupted files
. If some files such as vnetsup.vxd, dfs,vxd files missing error displays when the system boots then in win98 we give command “sfc” (system file checker) at run and click on second option “extract one of the specified file” and give the name of the file in a box such as vnetsup.vxd and click on start. Then give location of win98 folder such as win98 cd or dump of win98 in hard disk. Then give location where to save this file. This location is “c:\windows\system” and then click on apply. Repeat this procedure for every file.



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