I just built the machine late monday night. Everything booted like it should. I loaded win7 yesterday and everything worked great. Loaded up programs and left the computer on overnight last night to run a backup at 3am. This morning the computer was still working fine, quiet and cool. The backup was still running at 5am. I was doing some simple browsing on the machine and all of the sudden it powers off, as if I had pulled the plug. Pushed the power button and nothing happened. My first thought was the power cable had come loose from the PSU. Checked all the connections and everything was solid. I sat there trying to think of what to do next (it was dark and I wasn't ready to fish around inside the case), and about 30 seconds later it powered on by itself.
It ran fine for a couple hours (from 5 til 7) after that. I left for work with it on and running cool and quiet. Today at lunch I ran by the house to check on it again and it was off and would not respond.
The only thing that shows that there is any life at all is that the external hard drives that are plugged in the usb ports are powered. When I unplug the power and/or flip the switch on the PSU, the lights turn off and then back on when I switch things back on. However, when I press the button on the front of the case, nothing happens.
From what I read, this sounds like a bad motherboard. Any other thoughts? Any way to test this out? What should I do next?
ETA I forgot to mention I opened up the case at lunch and checked the ATX power header and it was plugged and solid.
ETA II My hardware...
Intel Core i5-3570K
Gigabyte GA-Z77-D3H ATX
Pareema 8GB (2 x 4GB) DDR3-1600
Western Digital Caviar Green 1TB
OCZ Vertex 3 120GB
Win 7 Home Premium
sounds like the power supply could not handle the light load and failed. mb and cpu if they over heat would flash a warning (bios) and shut off. most time you have to wait 10-15 min before they cool off. if they start overheating you would have gotten a flashing warning. shutting right down sound more like one of the legs of the ps failed. if you have a local show that has a ps tester or micro center the can see if one of the legs of the ps failed...if you have a friend that has a spare unit you can try the spare.
When you say it could not handle the light load, are you saying it is a faulty PSU or an incorrectly sized PSU for my build?
How interchangeable are old PSUs? I have a 9 year-old machine that this new one is going to replace that I could borrow for a bit if it would connect and not cause further damage. I'd rather not take that machine apart though, because I still have a need for it. I also have a machine that is even older than that (14 years?) that I could use.
If you are doing a full backup, you shouldn't be using the computer until the backup has completed. I'm unsure of the consequences of doing so as I've never heard of anyone actually running programs while doing a data backup however, all the resources of the system are in use during the backup and it could be that you have somehow caused a power surge in your PSU.