I have the MSI 785GM-E51 mobo with AMD Phenom X4 925 and just finished building it. When I press the power button on the front of the case, the PSU and system fan turn on for 1/2 second and then turn right off again.
I've checked all my mobo connections to all devices, including all power plugs etc. I've reseated my CPU and RAM, and even cleared the CMOS chip. Then I ran to Fry's and bought a new PSU and swapped it out to make sure it wasn't the PSU, but I get the same result with the new PSU. I've tried the same power plug and outlet into another PC and it starts right up. This means I've eliminated the outlet, the power plug and the power supply as the problems. My guess is it's something with my MSI mobo.
Please any help would be greatly appreciated. I've done a few builds several years ago but clearly I'm out of practice.