My parents desktop is shutting down randomly at various, unpredictable time intervals without warning. I have automatic restart on failure disabled, but no BSOD's are being displayed, the PC simply shuts off. Restarting the computer requires that I actually turn the power off to the power supply using the on/off switch on the power supply. Until I do that I can push the power button for the pc all I want and nothing will happen, but once I toggle the PSU switch, I can push the button and the pc starts normally. I haven't noted any boot problems or other issues (pop ups, missing files, etc.). My first guess is the power supply, but confirmation or other suggestions would be greatly welcome. I am decent at troubleshooting but am still a novic e when troubleshooting these kinds of problems.
The PC is a custom build as follow:
P4 @ 3.4ghz, low end mother board, 2 gb ram, low end ATI graphics. Nothing fancy, the pc used primarily for web surfing, word processing, email and simple, non-resource demanding games (yahoo, etc).
Thanks for your help.