Lol connection problem (possible fix)
If you can't connect to the loading screen try the above.
Servers are busy, lotta people tryin get in. Keep spam reconnect and you good.
If you got a black screen, try converting both resolutions to the same; there might be a display problem.
You can try making it windowed too from client options or ALT + enter.
Also, if that doesn't work.. make sure you aren't alt tabbing a lot when going from champ selec. to loading screen; that can cause it.
If you do get a black screen, a possible fix would be to end all LOL tasks from task manager and reconnect again. Don't watch youtube or Mia khalifa just let the game load..
Good luck