Why is my desktop shutting down (power off) on its own after an hour of operation?
 

This is what I've done:
1) reformatted hard disk and reinstalled OS
2) Scanned for virus
3) Cleaned the processor heat sink/fan. Reapplied new heat dissipation paste under the heat sink.

BTW, its a P4 processor, running on XP. Hope to get more leads as I'm running out of ideas. Cheers. Thx.

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