Screen goes black after game

The screen goes to black after game and freezes. my second screen is fully functional. but I can no longer tab out of my first, it is frozen. I need to keep my task manager on the second screen now in order to be able to end league as a task. It doesn't happen every time however. I have yet to determine if there are specific causes leading up to them, though if there are I cannot see what. it feels kinda random