I've searched the forums for a similar problem but can't quite find one that matches my situation. I had a bit of a scare today. I went to turn on my several month old rig and nothing happened. I saw that there was no power getting to the mobo (mobo and video card lights were both off).
My computer goes through a CyberPower UPS, and everything else connected (monitors, speakers) seemed to be working fine while the computer was not. I reset the power supply switch and also tried other plugs on the UPS but nothing worked. At this point I was pretty sure it was the PSU so I dismounted it and tried it on another computer. Surprisingly I was getting power and I can't say I was happy as my next guess was a mobo failure.
I brought the PSU back to my main computer and plugged it back in to the mobo only this time, and it was working again! I then reassembled the rest of the power plugs and got the computer running and have had it up for a few hours now.
The wall outlet is used for my UPS and a laptop I keep plugged in. Again, my computer was working fine for several months until today. The one thing I did not try before dismounting the PSU was plugging the comp directly to another wall outlet - I was using the UPS the whole time.
I was wondering if this is a non issue or if it's something more serious that I should look into? Could it have just been the wall outlet momentarily going crazy? I can't see how though, as the UPS was not running on battery power at any point and all other peripherals connected to it were powered.