Have you tried running your build with the least amount of components? if you have not, I would try unplugging all your case fans, extra HDD's, optical drives and even the graphics card if you have onboard graphics.
At first look, it sounds like a bad PSU. If there was a problem with the main board, specifically the main 24pin connector, I would think the fans would run normal but the computer would not post.
Do you have a multimeter you can test the voltage and such?