Your computer could be getting too hot. Download SpeedFan and check the temps. If the cores are under 50 degrees C, you're OK, over 65 is a problem, in between bears watching.
When checking for viruses note that some viruses can hide themselves from your antivirus program in normal mode, so you really need to scan in Safe Mode. To get into Safe Mode when you first power up, hit F8 about once a second until you get the menu and select Safe Mode. Then run a full system scan.
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Good luck.
computer shuts windows down but computer stays on I ran 2 different anti virus diagnostic with negative results.happens every 20 to 30 min cleaned cpu very good....problem still persists ran full scan with norton 360 found no issues

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