Hello. Just put together a new build and the PC just restarted after playing a game for 5 minutes. Now, when I try to switch it on, it boots for a few seconds then cuts out... then starts again. Though I can't see anything due to the GPU not powering up. There's no onboard graphics on the mobo but I've tested a spare card and that won't power either. Oddly enough it did this when I first tested the finished build with the sides off, but I checked the connections and THOUGHT I solved it, until I tried a game. Does this mean the PSU is faulty? It's a Corsair RM750 which I'm sure is enough to power the PC. Full specs below, I appreciate any help.
Asus X99-S
i7-5820K LGA2011-3
Corsair Veneance 16gb Ddr4
Ocuk GTX 980
Corsair H100i
Corsair RM750
Asus X99-S
i7-5820K LGA2011-3
Corsair Veneance 16gb Ddr4
Ocuk GTX 980
Corsair H100i
Corsair RM750