Game Locks up when game starts. [Please Help]

After the loading screen finishes and the game loads a split second after the champions appear into game, the game locks up and i cant close it, or alt tab. the only thing i can do is go to the windows 8 menu and log off the computer and back on. This does not happen when reconnecting, only when joining the game for the first time. I have repaired my client and it DID NOT fix this problem.

This means that as soon as the game loads i have to log off and back on then log on to league and reconnect every match.

The only map i have experienced this on so far is Poro King.