Building computer power won't stay on

[Alwayssbored]

I recently put together a computer.
Asus K8N
Athlon 64 2800
WD SATA HD
and the list goes on

Big probelm now is that I hit the switch on the case and the computer will be on for a moment and then turn back off. It will stay on long enough for fans to spin and that is about it. Not sure where to start troubleshooting. I check to make sure I had all the case switches in the proper pin slots. Any suggestions would be appreciated. If i'm being way to vague please ask for more info i'm just lazy.

 

[montag451]

check that nothing is shorting out the mobo -
loose screws, misplaced metal riser underneath the mobo, badly placed jumper.

take out everything from the box, and reconnect.
try the mobo connected up, but, on a cardboard box - not in the case