are you plugging your power sw, reset sw, hdd lines in correctly into their respective places on the motherboard? If you're positive they're in the right places ... could the wires be in backwards? i.e. green/white instead of white/green
When attempting to power on ... looking at the motherboard ... is your CPU fan turning on? LED's coming on?
I'd take everything out and just have the motherboard in with the cpu and a stick of memory ... not even a video card. Just see if you get the cpu fan powered on and some LED lights. If you do ... then add the video card and watch for a BIOS post. Then continue adding until you're loading your O.S.
ac'97? That sound card related?