Shutdown without warning. Its not a bluescreen

I have a windows vista with SP2. Sometimes I'll be on the internet or what not and all of a sudden the computer shuts down and restarts. It's not a blue screen of death or anything. It would use get a Blue screen of death before I Updated to SP2 but now It just shuts down without warning and restarts.

Hello,

It's most probably a overheating problem or hardware failure pointing to the motherboard. Ensure that your computer has good ventilation, nothing are blocking it's vents, no dust etc.

Ok thanks. But, how do i find out if it has a hardware failure pointing to the motherboard? Should I go to a professional to find out or can a software or program find out, or can i just do this manually; because I'm pretty sure it's not a overheating problem cause I'll use it for about 1 or 2 hours and it shuts down. Also because I've used the computer for 5-6 hours and it won't restart
So what do I do Doctor Inferno?

Hello,

Another possibility could be malware. Read this: http://www.geekpolice.net/-t3821.htm

And open a new topic here for a checkup: http://www.geekpolice.net/virus-spyware-malware-removal-f11/

If the Tech from the malware removal forum says you computer clean of malware then it should be a motherboard, or power supply unit (PSU) problem which would be difficult for us to troubleshoot because of the lack of testing parts.

Ok thanks then ill probaly just clean the vents in the computer and make sure thier is no dust because theyre probaly os becuase I havent cleaned it in about 3 years.