I know this sounds really dumb, but I had this problem....A little history first...I built my computer, checked everything, and it was good to go...I plugged it in, turned it on, and there was a huge spark from the PSU...I posted on here a ton, and sent the PSU back and got a new one (it turned out that my original PSU's warranty seal was never put on, and it must have been a faulty one to begin with). I got my new PSU, put it all together, and turned the PSU on. My fans twirled for 2 seconds, the light on my mobo came on, but nothing else happened. I got all freaked out, thinking my mobo and everything was fried from the first spark....Then I realized I had to push the button on the front of the computer, the on/off button...Man, I felt like an idiot...Just thought I'd share that story, to make sure your not doing the same thing....Have a good night,
Derek