My guess is the PSU and CoolerMaster PSU's being crap. My last PSU was a CoolerMaster 850w and had an occasional issue where my system wouldn't boot up unless I unplugged and replugged the power thing, and I don't have that issue anymore with my new 1200w SilverStone Decathlon
Also try testing each card individually, and see if the problem still happens, for it might be an SLI issue