League is freezing

hey. so my friend has recently been having troubles with his league freezing computer every game between 10 and 20 minutes into the game no matter what lane champ or role . Usually it happens if something big is happening on the screen like a team fight or multiple people taking drag. the screen freeze is permanent but he does not lose audio. When this happens he cannot even do anything else on his computer it is just completely frozen and the only way he can fix the issue is by Ctrl + Alt + Delete and restart his computer. When he restarts everything is back to normal. he loads back into the game and plays the rest of the game with no issues. Anyone have any suggestions?