Game Freezes during game

Im on windows 7. I did not have this issue until today but every time the new game starts, after 2 min screen freezes. I am able to move my mouse and access to the ESC menu but champions and minions won't move. Every time this happens, Im forced to quit game from ESC menu and reconnect but after 2min this happens again. i feel so bad for my team mate and don't wanna get banned because of something that i could not control. please fix this bug or at least tell me how to fix it. Thanks