Answer to "Not booting, red lights on ram board and processor warning lights?"So this is a super old thread, but wanted to chime in on this problem just in case someone else has this problem now and the above doesn't work for you. I just experienced this with my Mac Pro 5,1 mid-2012. I was getting no response when trying to turn it on with the power button and the CPU OVHT A & B red lights were blinking on the inside. The first time it happened, it turned out it was partially a RAM issue - checked the status of the sticks and one of them wasn't being read (under the Memory tab in "About this Mac"). Removed two sticks to keep it even, and that pretty much worked, but the problem eventually returned. What finally worked was doing the SMC reset technique, but making sure to remove all peripherals except mouse, keyboard and display so you can narrow things down in case this is all due to a hardware conflict. In my case, it turned out to be my outboard sound card. Completely solved - Mac powers up like nothing was ever wrong.