Thinking that I could learn a lot and not spend a fortune in a disaster, I bought some used 5620s and got all set to work on my 2009 cMP while dreams of 36k gerkbench scores and 5590s danced in my head. The install was problematic only in so far as the thermal pad material in that it is messy, not adhesive, and 5mm is not enough to replace (even double wasn't enough!) the original material. Yesterday, after resetting the smc and pram, it turned on and saw one processor. I even got to print the system report and then...WHAM! Out like a light. So this morning, I redid the thermal pad (processor B's did not look like it was making contact) and smc and pram and I even got to geekbench! The score was an improvement of more than 1000 pts! Then, WHAM! Again, out like a light! The fans are both working and responded to SMCFanControl so, thankfully, it isn't the heat sink fans. It sees both processors today so it isn't the sockets --I was worried because pin damage is the source of many horror stories. I thought I had the tiger by the tail but something is wrong but what? I get that the shutdown is protective but what is it protecting? The fans are working and the temperature is less than 100F (boost a) when the shutdown happens. Has anyone had this happen to their cMP? Update: As of 1226 mst she won't boot to the chime so I can't boot to a hardware test. Update: 1316 mst and still no boot to chime. Anybody think it could just be a coincidental failure of the power supply? If so, how would I know or how could I test it?