Sounds like an issue with your card, you might want to try switching manufacturers if this is a repeat issue. Your computer is shutting down to protect itself, your temps must have been going beyond the maximum recommended limits. Assuming you monitor them, what were you pushing at the time it shut down? You will also want to look into a custom fan profile, I had to do that for my GTX 660 because the factory fan profiles are pretty useless. I don’t really push past 70-73 C with everything set to Epic in realtime.