System Build -- New problem i've never encountered

[njc]

Built the system, go to fire it up, everything turns on (fans, etc), it runs for a long 5-6 count, and then just switches off, i really don't know much about troubleshooting before anything even comes up on the monitor (no beep codes, i'm pretty sure the speaker's hooked up properly)

Any ideas?

 

[MjrStryker]

Could you maybe give us some more specs of the system?

 

[njc]

P4 3.2
Antec PSU/Case
pgi DDR2 2x512
Seagate SATA HDD
Asus P5GD1-VM (onboard sound, video)

a pretty basic system