Recurring System Error

Over the course of the last week or so I have had the game crash on me. Not disconnect, not lag up or freeze; it's been a full on system error. If I'm lucky, the game will close itself and send an error report. More often than not? The game just completely freezes. Screen goes still, no music or sound effects, yet everything else seems fully operational. But because I play the game in fullscreen, it freezing up means I can't tab out or close the game short of signing out or restarting. This has happened once a day (at least) over the last several days, meaning it happens consistently. It's happened regardless of game mode, regardless of champion.