FULLSCREEN MODE / OUT OF RANGE

Hi I just bought a new monitor and whenever I try to play LoL in fullscreen i get these problems:

Getting a blackscreen when loading into game Getting an "Out of Range" error Other symptoms of audio working, but visuals not showing

I know i can play in windowed mode or borderless by using Alt+Enter on editing the config, but on fullscreen the games runs more smoothly and I dont have any framedrops, besides windowed.

Sorry for the bad english <3