crash problem after picking champs in lobby

I pick my champ and when game starts it goes black and stay black. later message pop up saying I cant connect to internet. the game say I crashed and I try again, but no good. I tried the shift and enter idea, check to make sure another copy not running. I tryed quit out and relogin and no good. somebody please help. my internet good and I can play with friends on private game, but not on online or bots.