well its unlikely to be the CPU, since the motherboard would have a set of beep codes for that, plus the harddrive would be spinning if even with the CPU working.
Try and take out all the memory, and turn it on (make sure there are speakers or headphones plugged in to the motherboard) and see if there are any beeps
well, so far it sounds like a bad motherboard to me since it should beep if there is no memory present, but, then again it might be the PSU not giving enough power to it.
is there any way you can change the power supply and try one from another computer, then try and turn it on?