All agreed, but the blank display was happening after just a minute or so of very undemanding games, such as Prodeus. The PC itself hadn't frozen, it just stopped outputting a display. I could still hear the audio that said that the game was continuing behind the darkness. The onboard graphics (Intel UHD Graphics 630) seems to behave, hence why my first port-of-call is to check the GTX 1080. If I don't find an issue with the card, I'll start looking elsewhere.