My custom pc (specks below) will sometimes shut down, with no warning. The issue started when I upgraded to a 780ti and my computer shut off while I was playing Brothers a tale of two sons (not a very graphically intense game). It turned back on so I thought little of it, but two days later same thing happened again, also while I was playing Brothers a tale of two sons, but this time my system did not turn back on, so I dropped my old graphics card back in (HD 7950) and the system turned back on. Before Doing an RMA with my 780ti I tested to make sure it was the graphics card causing the issue and nothing else. After thinking that the crashing issue was solved I went back to using my computer normally and sent away my 780ti to be replaced. But then while browsing reddit my computer shut off again, but this time the fans on my graphics card kept spinning, and turned up to 100%, I checked to see if hot air was coming off of it, but it was perfectly cool the fans were just spinning and the computer had to be turned back on by doing a hard reboot. The same thing happened one more time that day. Then the next day my computer shut off, but this time without the fan spinning and turned back on when I hit the power button. My computer hasn't crashed since (its been about a week), and I am still waiting on the RMA. I want to know if anyone has any idea what could be causing this, for I am scared to put my 780ti in once the new one comes.
i5 - 2500k
corsair 750w PSU
Gskill sniper series RAM (2x4gb at 1600mhz)
Old GPU HD 7950
New GPU 780ti