Getting completely locked out of my own computer when a game starts.

Sometimes when I start a game, the client has a critical error and a window pops up saying I need to terminate the process. Only thing is I can't do LITERALLY ANYTHING. The client stays permanently open and I can't move to any other window. The only solution is to force shut down the computer and completely reboot. Ruined my ranked TFT, but hey at least they got that new Death Recap, right?