I've had this issue as well. Sent in a support ticket, awaiting help from the tech team. In the mean time, I did manage to find something helpful. Apparently the freezing issue is related to a windows 8 security update. I found this elsewhere on the boards, and it worked for me, though it did give me a different issue in the process:
Okay if you are running windows 8 and have the freeze bug.
The latest Windows 8 update is causing the bug.
The solution is simple...
Just go into
Control Panel > Programs and Features > View installed updates
Find the one most recent..
most likely it has "security" in the name.
Uninstall it and run a restart on your computer.
After this your LoL should work just fine.
This worked for me, but now my homepage after logging in makes all the stuff there super large... I won't say the above solution is a permanent fix, but at least I can play again...