This is a problem to which i found no perfect solution on net. But here's what you should do:
1> check for all your power connections
2> check your pci-e slot for any loose ends
3> check if you have mounted all your mobo tray screws correctly
(to eliminate grounding issues)
Now if everything above is correct which i think is (just a formality
) try hitting the reset button after you turn on your computer and get the post error code 25. You will be cycled through the boot process and should be able to pass post error code 25. If it is successful you should turn on your computer by hitting the reset switch immediately after you hit the power button (everytime you turn on your pc!).
If this annoys you then consider RMAing your mobo and do tell me the results afterwards.