GA-P55M-UD2 won't power on

[vanteo]

I put together this build last Nov (so only 7 months old), with some of the pieces as recommended on Anandtech reviews:

Intel Core i5/750
Gigabyte GA-P55M-UD2
Antec TruePower 550 PSU
...

All purchased from NewEgg.

I haven't changed hardware or BIOS in months. I am not overclocking. I was using it fine just this morning. Now, it won't turn on at all. When I push the power button, LEDs flash once very quickly, fans try to start spinning up, but then nothing. The PHASE LEDs on the MB show green, green, yellow, red, but I can't find anywhere what that might mean (the user manual says they're only used for Gigabyte's DES2).

I first suspected the PSU, but all the voltages check out. I know that's no guarantee but, unfortunately, I don't have a spare lying around to swap in. I'm not quite sure what to do next. I submitted a question to Gigabyte customer service, but a phone number wasn't readily apparent.

Any ideas?

 

[mohonrim]

Did you check to make sure the power cord was plugged in?

 

[Powermoloch]

You pretty much need a spare PSU to see if the power supply is at fault.

If you have another computer lying around, I would recommend to use them as a test bed for the PSU to see if it can power up in a different computer.

 

[vanteo]

I pulled a PSU out of another box and proved it was the power supply that had failed. Turns out the PHASE LEDs show green, green, yellow, red, even when the motherboard is functioning fine.