This same question has been replied to (PSU or heat) in Computer Help: http://reviews.cnet.com/5208-6122-0.html?forumID=44&threadID=159283&messageID=1768158
I lock this thread to keep the discussion in one place. Any other ideas can be posted in the other thread.
First here is my system
Asus p4p800e-deluxe motherboard 865pe chipset
intel p4 3.4
ATI Radeon x850 pro video card
1.5 gb ram
All I have to do is run virus scan and get on the internet and it crashes/reboots. Or try to play any game with decent graphics. My daughter gets on to play her sims game and it reboots 5 min into it. It actually crashed while running the screen saver. If im just browsing the internet or doing everyday stuff it is fine, but the second I do anything that puts any sort of pressure on the cpu and or video card it crashes. Maybe a video card problem or a overheating cpu. It gets to about 60c and then dies. Help Help. Any ideas? I have updated the drivers on the video card and updated the chipset drivers on the mobo.