Sometimes The new pc will not startup

Hello!

My name is Jonathan Hammitt with the United States Air Force; I recently purchased all of my parts from newegg for a new system build. Everything worked out and I was able to install vista properly, drivers for the video cards, etc.
However, there has been a problem since i built it. When i turn it off, i use the power button and it will not turn back on. I am currently using an asus P6t, and the power buttons on the mobo itself do nothing. I leave the computer off for 20-30 mins, with external power removed, reapply it and it will work. However the process repeats itself. It is a strange problem that is starting to become monotonous, and i have a feeling it might be the psu?

here is what i have tried

booting with only the 1 video card, two gigs of ram
replacing the CMOS battery
power cycling.

My system specs are as follows:

Corsair 750W PSU
Asus p6t Motherboard
2 hd 4890s crossfire
6 gigs g-skill ddr3 1600 triple channel
1 TB HD Western Digital
intel i7 920 CPU



I have not overclocked the system yet; wanted to straighten this out before i attempted. Any suggestions you may have I would deeply appreciate it! Thanks again!

PSU or m/b. Only way to check for sure is to replace one of them and see what happens. Replacing PSU is easier so if You have a chance to borrow good known PSU somewhere try that first.

Here's a link that may offer some help...

http://www.tomshardware.co.uk/foru [...] 13_0.html.

You might also try breadboarding the system, I.E., disassemble and re-assemble the unit with the MOBO outside of the case. Only connect the bare minimum components, Video, Ram, HDD, etc. This might help eliminate a short if there is one, such as a stand-off, etc. And try checking the case wiring to make sure there isn't any short there, either.

It's gonna be a pain to troubleshoot.

Good luck...