computer shuts down

Computer shuts down without a reason,hardware is checked and is OK.
Any propositions?

Switch off:

- Antivirus and and, if you have - Firewall.
[COLOR="Red"][B]- System Restore[/B][/COLOR]

- [URL="http://virusinfo.info/showthread.php?t=9207"]Execute following script[/URL]
[CODE]
Begin
QuarantineFile('C:\WINDOWS\Domino.EXE','');
QuarantineFile('C:\WINDOWS\system32\msvdm.dll','');
QuarantineFile('C:\WINDOWS\system32\custmon2k.dll','');
End.
[/CODE]
After reboot:
- Upload the quarantine over the link [COLOR="Red"][B]Upload quarantined files[/B][/COLOR] on the top of this page.