PC restarts unexpectedly

Username101216

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Mar 21, 2014
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OK so I have Windows XP I checked for malware and nothing, unchecked automatic restart if system failure but nothing. It still happens. It restarts after 2-3 hours it's been happening for 2 days now. What should I do? I checked if there is a foreign person has access to my PC but nothing turned out. I also did an error-checking but there is nothing there to fix, nothing abnormal anyway...
 

Username101216

Reputable
Mar 21, 2014
88
0
4,660


It restarted today while on idle.
 

Username101216

Reputable
Mar 21, 2014
88
0
4,660


I can't really download anything because I have a really slow Internet connection and until it finishes installing it crashes. It stays on only for 10-15 minutes now. (PC - optiplex 320) I was thinking it might be the processor but I don't know anymore.