ok...
first, take out all pci cards, all ram except 1 stick, hdd and opticle drives (ide/sata and power). try post. if it still doesnt post then check the case speaker is plugged in.
plug in the power to 1 opticle drive and see if the drive boots (lights flash, it spins up, then sleeps). if the drive doesnt boot up, then swap out the psu.
if the drive did boot up then take out all ram sticks and attempt a post, if the case speaker works then it should beep continously (with brief pauses), we may not have a dead motherboard.
if its still not posting or beeping then swap out the cpu, or the motherboard.