You can try and disconnect all of your drives, including your hard drive and see if it will boot. If it does you have a bad drive. In fact the machine I,m using right now has somewhat of the same problem. Turn in on and only get a two second burst then everything goes off. I found that the primary hard drive has a problem and is killing the power during the post.
In fact you can even pull the memory out and it should post but not kill the power. if you get to the point that you have nothing but the motherboard and it still will not power up, disconnect the power and then unplug the power connector from the motherboard and use a jumper and connect any of the black wires to the green wire, then reconnect the power. DO NOT plug the connector back to the motherboard. With the jumper in place your power supply fan should come on and run.
If you find you have a bad drive just reconnect them one at a time untill it fails to power up and then you have found your problem. Good luck and let us know what you find.
