Power keeps going on and off

[crossbone]

First off, this is my first attempt at putting together a system. Pretty much everything is new and here're the specs:
mobo: gigabyte ga-ep35-ds4
cpu: intel e8400
memory: 4gb
psu: 650W Cool Master Real Power Pro RS-650-ACAA-A1
graphic card: Geforce 9500 GT

Problem: pressed power button, all fans run but 1-2 seconds later, everything shuts down automatically before restarting. this goes on periodically and I can't figure out why. is it a faulty power supply? bad mobo? short circuit somewhere? or problem with cpu(checked and made sure heat-sink is securely fastened)?

any suggestion will be appreciated.t
thanks!

[mjc]

Are all the auxiliary power connections connected?

Pull everything from the case, setup a minimal (CPU, one stick of RAM, power, case speaker if the board doesn't have a built in speaker...no drives, no video, no extra cards) environment, on a piece of cardboard. If you get some life...start adding in more items. If it passes on the cardboard, then put it back into the case...