Problem with PC rebooting

[tommy0628]

Hey everyone, i recently built a new PC

3.0ghz Pentium D
Intel 945 mobo
ATI All-In-Wonder 2006 edition
1gb OCZ ram
coolermaster 550w powersupply
windows XP media center edition


Here is the problem i am having... My PC will run continuously for 4-5 days at a time, then it will randomly re-boot and the ATI card no longer is my primary video adapter... It uses the onboard video even though i have it totally disabled in the BIOS.. The ATI will not work until i completely power off the system and start it back up.. then everything comes back normal.. I get no blue screen, no nothing.. Im sure its something to do with either the Powersupply failing out, the CPU overheating, or the Video Card overheating... Its just weird that it runs for 4-5 days non-stop with no issues.. And it only reboots when its idling

Things ive tried
uninstall ATI drivers completely and re-installed them
took out video card and re-seated it


If anyone has any other ideas it would be helpful, this is driving me nuts... my old pc that i built would stay for 8 weeks at a time but this one wont make it past 1 week.

[pam123]

The next time it does that check Event Viewer for any errors that occurred at the time.

[tommy0628]

checked the event viewer... nothing shows up out of the ordinary. I have "Automatically Restart" unchecked so i know its not bluescreening. Im almost certain that somethin is overheating whether it be my CPU or my Video Card... Would it write an event to the system log if it rebooted due to overheat?

[pam123]

No it wouldn't.
Do you have any four-feet at your place ?
If it's safe then a day or so before you expect a reboot take the side off the case.
No reboot means you guessed right about the heat.

[BrokenKingdom]

Run a program like prime95 or play a game with decent graphics for a while. Basicaly get your pc to run full load for a while if it shuts down then it's a problem with over heating.

If it doesn't then your problem could be power surges a lot of places have fluctuations that cause the same type of behavior.