I only got my card today and I have had this happen.
I have played WoW for a short time, played dark souls 3 for a while and modded skyrim with latest enb builds requiring 970+ for around 2 hours.
Loaded up guild wars 2 and roughly 20 minutes until the screen goes black and the fans ramp up.
I dont want to RMA this, as I have only just got it. Im hoping it is just some issue with guild wars but would need someone else to comment on this.