If your machine is constantly shutting down/restarting, it could be viral related or could be due to hardware or overheating problems caused by a failed processor fan, bad memory (RAM), failing power supply, underpowered power supply, CPU overheating, motherboard, video card, drivers, dirty hardware, etc.
However, try a couple other scans that are not as resource heavy or stressful to your system. Download and scan with
MS Malicious Software Removal Tool and with the
Vcleaner Tool. Be sure to restart your computer in "
SAFE MODE" and then run Vcleaner.
If you can complete those, then download and scan with
DrWeb-CureIt. Follow the instructions
here and see if you are able to complete the scan.
If your not finding any malware then its sounds like the latter problem.
When was the last time you cleaned the inside of your computer? Dust restricts the airflow and prevents proper cooling. This in turn can cause overheating and faulty processor fans which can result in unexpected shutdowns, random restarts, booting problems, etc. Open your machine and make sure the fans are working and the heat sink on the processor is not blocked with dust or debris. Remove the CPU's cooling unit and clean the fins on the heat sink that sits under the CPU with a can of compressed air. You can also remove the cards, RAM modules, clean the contacts and reseat them. Check your connections and fans to make sure they are working properly and monitor the temperature. If the computer is overheating, it usually begins to restart on a more regular basis. See "
Cleaning the Interior of your PC" and the "
Illustrated How to Replace an AGP Video Card"
(you can also use it as a guide to clean & reseat).In Windows XP, the
default setting is for the computer to reboot automatically when a fatal error occurs. You should be able to see the error by looking in the
Event Log. An alternative is to turn off the automatic reboot so you can actually see the error code/STOP Message when it happens -
this is also known as the Blue Screen Of Death (BSOD).To change the recovery settings and
Disable Automatic Rebooting, do this:
1. Right-click on My Computer and select
Properties >
Advanced tab.
2. Under "
Startup and Recovery" click on the "
Settings" button and go to "
System failure".
3. Make sure "
Write an event to the system log" is
checked and that "
Automatically restart" is
UNchecked.
4. Click "
OK" and reboot for the changes to take effect.
Doing this won't cure your problem but instead of restarting you will get a blue diagnostic screen with information displayed that will allow you to better trace your problem. See "
Extract troubleshooting info from Windows XP BSOD error messages" and
How to Find BSOD Error Messages. Also see "
Windows XP Error Codes", "
Events and Errors Message Center" and "
Troubleshooting Windows Stop Messages". If you don't find the error code you have in any of these links, then try doing a Google search of it.
Download and run
Motherboard Monitor 5. If Motherboard Monitor's seems to be reporting high temperatures for your CPU check to see what your max CPU temp is from
here.
There are suggestions for
troubleshooting power supply, video card, CPU, RAM, MB and hard drive here and
here.
You can also use
BurnInTest to stress test the CPU, hard drives, RAM, CD-ROMs, CD burners, DVDs, sound cards, graphics, network connection, printers, video playback.
This utility works on all Windows versions to include Vista (32-bit & 64-bit).
Another option is
Microsoft's Online Crash Analysis. The Windows Memory Diagnostic tests the RAM for errors with a comprehensive set of diagnostic memory tests. Also see
Memtest86+ and
Memtest86.