Login Screen stays black

So ive tryed to follow what you said to do but the login screen isnt fixing ive reinstalled league so many times and the login screen stays the same. Ive tryed just about everything and nothing has changed.This is a really annoying bug i don't know how it started because my league was working fine till now. I log in one day and login screen doesnt poppup so i just think i have ti restart my pc still didn't. i just wanna play league again