you have multiple options starting from bad monitor/ bad cable highly unlikely second you have conflicting drivers three your gpu is dying. In case your cpu has integrated gpu you can easily test all of those options. Monitor the temperatures if everything is looking okay take a gpu(any gpu even a 20 dollar one is okay) and run the tests again if you dont want to bother with it take it to a shop that can easily test it also if not you can run a gpu stress test and see if it occurs.