OT: vexing hw issue

[Dave Stevens]

I want to make a new Fedora box so I used an existing case and put into it a 
new ASUS motherboard and a dual core low power CPU (an AM2+) and 1 gig of RAM 
(512x2) and a new 450 watt power supply. The only front panel connection is 
for the power switch. Every time I power up (wall power is known good) the 
unit goes through all the motions for about 5 seconds then stops dead. It 
never gets to powering up the on-board video or doing the ram check or 
displaying the BIOS config messages. Tried another PS with the same results. 
Any ideas? I mean ANY ideas, I'm out of clues on this one. References welcome.

Dave