Computer Reboots (ruled out virus, malware, spyware, etc)

Okay fellas, I need your help. My computer reboots itself randomly. I went to the spyware forum and received help from Chaslang and we have successfully ruled out spyware, virus, malware, etc. He thinks it's software related.

The problem I'm having is: when my girlfriend sisters go to myspace.com the computer reboots. I've had problems with the system rebooting when I went to g4tv.com. I've gone to other websites in the past and its done the same thing. It's driving me nuts.

System info:
WinXP
2.8GHz
512 RAM

Someone mentioned that my fan might not be working but I'm not sure that is the problem because I can be online all day but the second I go to myspace.com the computer reboots.

Any help I can get is very much appreciated

 

Did you try a repair internet explorer ???

 

The problem persists even in Mozilla Firefox so I'm not sure its an IE problem.

And I have all the current windows updates.