Game constantly freezes during character select screen and in-game

Recently my game started freezing during the beginning (legend select/champion squad) and in a middle of a match. It mostly happens in ranked but it's probably because i don't play much casual. When i alt-tab during the freeze the game window either goes black or white, and when viewed in task manager it uses 0%-1% CPU. I cannot close the game window without using the task manager and i cannot alt-f4 out of it. The only fix i found was alt tabbing during the char select screen but no fixes for in-match freezes. Please help, i fear i can't play ranked anymore because i may get banned for something out of my control