Champion select not coming up after accepting game

Third time this has happened to me. I click "Accept" to go into a game, I get the "BINK!" sound as the champion select window opens, but all that comes up is a black screen. I have to exit the client at that point, champion select screen never comes up. I get a warning about leaving and I do in fact get a penalty (which bugs the CRAP outta me as I didn't do anything wrong).