game freezing and have to sign out or restart computer to fix

I will go through champ select just fine load it nice fast and in a hurry and then about 10 seconds after the game starts the entire game freezes i can't alt tab, i cannot alt f4. The only thing that worked for me was to sign out or restart my computer and load back into the game. I have uninstalled the game twice with a full wipe I have also repaired the game at least 3 times. I have never had this problem before and its really affecting my games by missing the first two and a half minutes of it at least. Some assistance would be more than appreciated. Thank you for your time and consideration.