Two possibilities (and I think #1 is the most probable):
1. Heat. Take off the case, blow a household fan on it and see if it makes a difference. If so, clean the fans or have a tech install better ones.
2. Insufficient or detoriating power supply. Replace.
Hope this helps.
Kees
Pc Specs:
P4, 526 Ram, 80GHD, XP Home edition SP2
Pc switch off when using DVD Factory, or any other high processing program

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