To update – i have resolved this issue, but am very sure that premier pro has a bug specifically relating to changing (ticking/unticking) GPUs in the (preferences->media) settings.
I have come to this conclusion because – i spoke to Nvidia who told me to remove the driver with there clean-up tool, and do a clean install of the driver. After doing so i then tested and all was back to normal (with my settings as seen in screenshot 2). i then changed the settings here to include the intel gpu. It then didn’t work. So i went back to just having Nvidia ticked, and still nothing!!!
After completing the removal and reinstallation process for a second time, i haven’t changed the settings and all is working fine.
I’m hoping no-one else has this problem, and therefore don’t read this!!!!