Follow the troubleshooting instructions in
this thread...you
must remove the motherboard from the case when doing this...you're trying to determine if the motherboard is shorting/grounding out to the case. Make sure you don't have extra standoffs installed in the motherboard mounting tray...whatever standoff installed must line up to the motherboard mounting holes (the holes with the metal ring around them). Any extra ones have to be removed from the mounting tray.
Cricket