Can't even load into the game

Every few games I join and start loading in, I get to 100% and then nothing.. then the game just crashes my whole computer and I have to physically unplug it just to get it to reboot and try to get back in the game. Of course this takes a good 6 minutes so by the time I get in game is already over and I'm getting in trouble for "afk behaviors".

Even if the game lets me play I'm suffering from massive dips in frame rate. Has been happening for a few months now and Riot has done nothing to address it.