League won't tab after game starts

I start a game of league, and once everyone picks their champ and the launcher closes, that's all I see. Usually you see the League of Legends logo and then the loading screen with everyone's champs,and then eventually the game but this isn't happening for me. Then when it gets in game I hear noises from the game, but can't tab open the game. I've tried Alt-Tab to open the window and the screen turns black like it's going to work, and then my desktop appears. I tried clicking on the League button on my task bar to open it and the same thing happens. I've tried restarting my computer but that didn't work, and I even uninstalled and reinstalled League. Nothing worked. League worked fine yesterday and only today when I turned on my computer to start a game this happened. Has never happened before and I haven't done anything differently to my computer. Anyone have ideas on something else I could try? Or is anyone else having this issue? Thanks and much appreciated....... Without League my life is POINTLESS!!! :'(