First Boot Problem- light/fans shut off in half second

Hey so I helped my roomie out with his first build. We got it all in the case and pressed the power button. We got a flash of light from the PSU (which has a big blue light in it) and some noises from the fans and then it all shut down. No beeps, no video, no anything. We pressed the power button again and the second time didn't even get the flash of light and fan activity.

The parts are as follows:
Mobo: ASRock P67 PRO3 (B3)
CPU: Intel i3 2120
GPU: XFX Radeon HD 6870 1GB
PSU: Raidmax 630W pseudomodular
RAM: G.SKILL Sniper 8GB (2 x 4GB) DDR3 1333
HDD: seagate barracuda SATA 6 GB/s 500GB
Optical: samsung Blu-ray SATA burner


So we opened the case and checked all the power connections and RAM to make sure it was in. Then we fired it up again while the case was open. This time we saw the power supply lights turn on and the PSU fan and CPU fan start to rev up (which we assume happened the inital try but just didn't get to see it). However it only got power for about a half a second and then it all shut down.

I'd normally try a different PSU in the build but I have no other PSU that can power the build with it's connections. Any ideas? Should I try to take something out to rev it up? Like run with less parts or something. (the GPU is needed for video output)

I've got no idea which part is the culprit as I've never seen the PSU give power to only shut off before. In my experience when the PSU gives out it never gives any sign of life on boot. My only idea is maybe the Power switch header is connected backwards, but would it cause this pattern of behavior? Any help is appreciated, thanks. If the RAM was bad would it give me some mobo beeps? if the CPU is bad it would too right?

Help is appreciated oh wise ones!

Sounds like you might possibly have a shorting problem. Is there by any chance a MB standoff under the MB that is not located under a mounting hole in the MB?

I'm having this exact same problem. Power for a split second then nothing. I'll look for a short.

Edit: Its because I never plugged the CPU plug in lol