My money would be on the motherboard rather than the PSU to be honest. The 660 isn't a power hungry beast at all, and your single 12v rail should handle it with ease. Though I guess if it's partially damaged and outputting a dirty voltage (i.e. fluctuating or inconsistent power out) then it *could* cause some issues? Again my money would be on the mobo before I suspected the psu
What I meant re the power cables is take your OLD pc, unplug the 6-pin power cord that goes into the graphics card, and try to plug that into the 660 in the NEW pc. Usually you have to put the cases right next to each other to get it to reach, be creative haha
Yes, all bios and chipset drivers are up to date. I guess I can give that a try.. I'm assuming both pc's would have to be on for old one to power the new one? I'm still really confused about this one.