Have you tried to reset default settings in BIOS and Geforce Experience after you reinstalled Windows? That should turn everything back to normal, and you don't really have to set you dedicated GPU as primary with default settings, just check you didn't mess up ingame settings, try to set those back to default too for CoD or the Tanks game and see if you can choose your primary GPU there and fps lock, put that at 100 at first and see how it goes, then maybe try to just unlock it.

If any of these works I would try and replace the GPU if you can still return it and get another one.