My 5,1 Mac Pro 6-core, 5870, 12GB Ram will no longer power on. Started when the system failed to wake from sleep today and had to be forcibly shut down. Now even after disconnecting the power cable for several minutes, it will only make a click noise when attempting to power on. Tried Mac Pro SMC reset (remove power cable for 15sec, plug in, wait 5sec, press power). When I remove the 3x 4GB RAM sticks it will power on, but does nothing. I've tried all RAM slots and the only one that appears to allow a RAM stick in with power turning on is slot 4 of 4. However, even though the power turns on, it does not reach the Mac chime (POST). I try holding PRAM reset buttons, but it obviously isn't even making it that far. ------ Anyone have any idea what part of this Mac Pro has died? I'm guessing not the PSU since it will power on with no RAM.