process of elimination
take the cables off your cd, hd and floppy see if you get a post message
if you do, add them back til you don't
if you don't, start removing cards until you are down to just the video card, ram, and the cpu
if still bad, swap out the vcard, ram if you have extras - try a new case (PS) if you have a good one to test with
make sure the motherboard isn't shorted to the case somehow ie loose screw rolling around in the case, etc..
gl