Answer to: Mac Pro 5,1 won't boot. No power, no noise at all, only a couple LEDs.I’ve repaired several 2010-2012 Mac Pros that have had this issue where the computer won’t power on but the LEDs blink. In some cases the graphics card has been the issue. Simply replace the graphics card and viola! In most cases however I’ve found the problem to be the Backplane / Logic Board. In none of my experiences has the problem been related to the power supply.