So you've tried resetting the CMOS, I guess that means the battery was disconnected with the power unplugged?
Try removing all of the internal connectors to the motherboard except power. (think HD, etc) Disconnect all of your external items except the keyboard and monitor.
Still no life - have you tried reseating the memory modules ? - perhaps a removal of one or more may isolate the problem to that.
Another check is to pull all of the cards but the video.
In checking the power, I get your meaning to be that every pin is producing the correct voltage and the grounds are at 0V?
With all of the above not working, it comes down to the processor or the mb or the CMOS on board the mb.
Good luck Emp !