Bug?? Mac

My game always crashes after champion select on my macbook air. It shows up "Game has crashed". When I tried to join again it almost immediately shows up "Game has crashed". My computer doesn't allow fullscreen applications and crashes it if launched. I tried to make my LOL windowed but to do so I had to go in-game to set it, but the problem is that I can't go in-game. So i am thinking about putting the "Video Setting" tab on where you can see the latest skin discounts, news yada yada. Or is there a way to fix it by digging into my laptop and setting something? Please help me :(