temporary black screen after going into fullscreen mode

so basically as the title states, theres a short period of time (about 5 sec) in which my monitor goes completely black after going full screen mode. i feel like this has to do with some tweaking i did a few days ago, trying to change my resolution. I’ve also been experiencing terrible frame drops when I’m in a fight and my camera angle is rapidly shaking however this was NEVER a problem up until now. does it have something to do with that ? i just want to revert my pc so it doesn’t do that black screen thing. i want to be back on native res (if I’m not already, because like i said i don’t fully know what’s causing the problem just assuming) and not experience the frame drops i currently am when shaking my camera as it was NEVER an issue before this i was always at a stable frame rate. any help would be very much appreciated. thank you.