Can't run 4k external monitor from my laptop

I have been trying to get my 4k external monitor displaying at 4k resolution for a while. I bought it in February and since then it displayed 4k perfectly, although a few weeks ago while I was running Virtual Desktop for a VR application, it changed automatically to 1080p. So I know the laptop can display to a 4k external monitor. Looking back I probably should have disconnected my external monitor while playing VR to apply less stress on my laptop. Since then whenever I select the 4k setting in Windows display settings, or NVIDIA control panel, it automatically reverts back to 1080p. I tried

Question by Kev17 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.