Try closing it the restarting it. That might help.
Yeah I get this problem from time to time. A good place to start is to try and install the game on a desktop or laptop as opposed to the potato you are currently using.
This happens to me as well, if it still is continuing, close LoL, restart your computer, and open it again. Sometimes it may take 2 or even 3 reboots to get it to actually load.