My PC won't start; what could be wrong with it?

If your computer won't start correctly, the reason often depends on what happens when you turn on your computer.

Electrical problems

The first step is to make sure the computer is getting power. When you try to turn on the computer, if you don't see any lights come on and no sound comes from the computer case, then your PC is not getting any power. In this case, check the power cables first. If your system has a 110V/220V switch on the back, make sure it is set firmly in the 110V position. Also, if you use a surge protector, make sure it's turned on and you are receiving power from your wall outlet.

If all of these connections are fine but you still hear and see nothing when you turn the computer on, the power supply may be damaged. In this case, you will need to take your system to a repair shop to have it diagnosed and repaired.

Note: Sometimes the cooling fan will spin even though the power supply is broken.

If the CPU lights up and beeps, but the monitor remains dark, make sure that the monitor is turned on and getting power (check for the power light, usually located near the switch on the monitor face). Make sure that the monitor, keyboard, and other peripherals are firmly attached to the CPU.

BIOS (CMOS) problems

If you do see the power lights come on and you can hear the hard disk start to spin, check to see if something appears on the screen. On PCs, there is a built-in program stored in the computer's BIOS (Basic Input-Output System) that checks all of the hardware when you turn on the computer. This is called the POST, or Power-On Self Test. The BIOS stores information about the hardware in your system in an area of memory that is not erased when you turn your computer off. This non-volatile memory is referred to as the CMOS RAM.

When the BIOS finds something wrong with your computer, it notifies you by flashing an error message on the screen or making your computer emit a series of beeps. These beeps are actually diagnostic messages. Different brands of CMOS have different beep patterns (see If my computer beeps and fails to boot, what do the beeps mean?).

Depending on the brand of BIOS that your computer has, any diagnostic messages that appear on the screen may be either informative or merely cryptic.

If the BIOS tries to access the hard drive in your system and fails, it will (in most cases) alert you to this fact. If the BIOS can't access your hard drive, that does not necessarily mean that your hard drive has failed or that you've lost everything on it. It's much more common that the BIOS has lost the settings for your hard drive configuration stored in the CMOS RAM. This is because the CMOS RAM is maintained by an internal battery, which has a finite lifespan (usually three to five years). When the battery dies, the CMOS settings are lost, and you have to get a new battery and restore the settings.

The settings in the CMOS RAM for your hard drive (such as the number of heads, cylinders, and sectors per track) depend on the brand and model of the drive. Many hard drive models allow several different configuration settings; however, if you use different settings from those used when the drive was set up initially, the drive will be inaccessible.

In most cases, a BIOS error means that you will either have to investigate your CMOS settings or swap components. Usually, you will need to take the computer to a technician. If the boot failure occurs after you have just installed or moved a video card, you should power down and push the card firmly into its slot, and then try restarting.

Problems with booting

If your computer gets past the POST stage, the problem is most likely something in the Windows boot process. At this point, it's useful to boot into Safe Mode or to use the Recovery Console (Windows XP) or boot diskettes (earlier versions of Windows).

Booting into Safe Mode for Windows 2000 or XP

If you can boot into Safe mode, you can set it to not load certain drivers, disable startup items, run ScanDisk, and use a number of other diagnostic tools. See In Windows 2000, XP, or Vista, how can I boot into Safe Mode?

Using the Recovery Console in Windows XP

If you have Windows XP you can use the Windows XP installation CD to reach the Recovery Console and access DOS (the command prompt). For more information on the Recovery Console, see In Windows XP, what is the Recovery Console?

Booting from a floppy disk in Windows 2000

If you have Windows 2000, you must use an Emergency Repair Disk created with the same version of Windows. See In Windows 2000, how do I make an Emergency Repair Disk?

Viruses

It may also be that your computer is infected with a virus. In this case, you should use an antivirus boot diskette to disinfect the hard drive.

If you are a student, faculty member, or staff member at Indiana University Bloomington, you may obtain virus boot diskettes from the UITS Support Center walk-in locations in Bloomington.

For information about Support Center walk-in offices (hours and locations), see UITS Support Center walk-in locations and services.

Your virus protection software, such as Symantec AntiVirus or McAfee, may have come with a virus boot diskette. Most virus protection software has an option to create a virus boot diskette(s) once the software is installed. However, you should make sure you create the diskette on a computer which is not currently infected with a computer virus.

See your virus protection software's manual or help files for instructions on how to remove a boot sector virus using the virus boot diskette(s).

Further troubleshooting

If you run a scan for boot sector viruses using a virus boot diskette and your hard drive is still inaccessible, there may still be something wrong with the CMOS settings for your hard drive, or it may be that the drive has indeed had a mechanical failure.

However, if you get the error message "Missing Command Interpreter", that means that the COMMAND.COM file on your hard drive is corrupt, missing, or has the wrong version number. In this case, restart your computer with the boot diskette in the A: drive. At the A> prompt, enter:

copy command.com c:\

Then remove the diskette and try rebooting your system again. If the computer still cannot boot from the C: drive, start it up again using the boot diskette. At the A> prompt, enter:

sys c:

This will transfer the system files from the diskette to the hard drive, hopefully making it bootable again.

Now remove the diskette and reboot your computer. Your system should now boot from your hard drive. If it doesn't, it's probably time to seek professional assistance.

Also see:

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Last modified on October 14, 2008.

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