My game wouldn't start after champ select (internet was connected).

I was in my last promo game and no where in the world would I ever intentionally afk or not want to play the game. I constantly pressed reconnect and it was just black screen. I was so worried that It wouldn't even turn on and it never did. My internet was fine other people were also playing league on it and nothing happened to them. My computer is also perfectly fine and I have no idea why this happened right before my last promo game. I got leavebuster for it and now I am really sad because I lost promos and got leave buster because my game wouldn't start up. If anyone can please help me and explain why this happened and how to prevent it from happening again I would be happy. Also is there any way I can get rid of leave buster because this was not my fault. I didn't intentionally leave the gave or afk it just wouldn't start. Please help!!