expected argumen 'c': can someone help me

when I press on launch a screen with expected argument 'c' pops up and i can't play th game i thought it would go away so i tried for 2 weeks everey day if I could get back on lol but I always get that same screen. does anyone know how I can fix thi and play my lol again? btw: reinstalling the game doesn't work because i triedd it a few times already