Random reboot - help!!

[rodasimmons]

I'm suddenly having problems with my PC that are driving me crazy. I built my system about 2 years ago and have had no problems with it until recently. The system constantly shutsdown on its own. Sometimes it reboots and comes back up, other times it just powers off. Sometimes it will run for 2 minutes before shutting down, other times it may run for up to 3 hours. When this occurs, Vista displays "Windows is shutting Down" and it goes down within 5 seconds. The only thing I see in the logs is below:

The process C:\Windows\system32\winlogon.exe (HOME-PC) has initiated the power off of computer HOME-PC on behalf of user NT AUTHORITY\SYSTEM for the following reason: No title for this reason could be found
Reason Code: 0x500ff
Shutdown Type: power off

The problem occurs when running windows and when running from a linux boot CD so it isn't not specific to Vista. So far, I have replaced the power supply and the motherboard. I'm a sys admin and have access to hardware at work. I have brought home differnt video cards, ram, and even a different C2D processor and the problem still exists!!! There is nothing attached externally to the machine and there are no cards in the machine other than the video card. The only component that has remained the same is the case. I've checked temp in the bios and the system and cpu temps stay around 28 - 30 degrees Celsius. I don't know what else to do. I welcome any troubleshooting ideas that anyone may have. Thanks in advance for your help!!

 

[jsc]

Breadboard the system:
http://www.tomshardware.com/forum/262730-31-breadboarding

That will isolate the case. If the system stays up, you know it is the case. If the system still reboots, you know it is not the case.

 

[capt_taco]

First guess would've been your motherboard or power supply is retarded, but it sounds like you've already ruled both of those out. I agree with jsc's suggestion to troubleshoot the case; if it's contacting the motherboard where it's not supposed to, or if there's a problem with the power/reset switch itself (or the connecting wires), that could be doing it.

One other thing that's rare but still possible: Does you keyboard have buttons for either sleep mode or system shutdown? If the keyboard is having problems, it could be randomly firing off one of those signals when you don't want it to. That was happening to me occasionally on an old P3 system I used to have, and it drove me NUTS trying to figure out what the problem was.

 

[rodasimmons]

Breadboard the system:
http://www.tomshardware.com/forum/262730-31-breadboarding

That will isolate the case. If the system stays up, you know it is the case. If the system still reboots, you know it is not the case.

The last thing to check was the power switch and that was it! Since the power switch it molded into my case, i've just cut the wires to the switch(leaving them attached to the motherboard) and run them through the front grill on the case. To power on, I just touch the tips together. The system is rock solid now and hasn't gone down since. Thanks for all the help~