Keep sometimes getting a black screen

I've recently purchased an Alienware CPU and I downloaded League, but I've been having some trouble. After I log into league and get into queue my game will sometimes just be black in the loading screen and game. It doesn't happen all the time and it usually only happens for one or two games but it is very annoying. I'm still in the game and can click, hear noises, and talk on league voice, but the screen is just black. I've looked up how to fix it and I've tried most fixes but it keeps happening. The main problem is sometimes it will work one game, but the next it will be a black screen and I've already ruined a ranked game for my team because of it. I don't know very much about computers, or anything really, so if anyone can give me a solution I'd be very grateful.

Thank you