Most of the issues with the 970's and some 980's are exactly the same issue as I'm having.
Here's another
thread about it, interestingly one of the last post's a guy claims to have upgraded to windows 10 and his trouble has completely disappeared (guess what I'm now downloading)!!
Running P Cars flat out this morning and boom 2 laps in and I lose my display, pc still running and the monitor tells me it's going to turn off as it has no source, hard reboot system and complete 5 laps of P Cars, same settings, same cars, same track and weather settings, it makes no sense.