Game Freeze?

So, while I've been playing norms and urf recently, my game has frozen in the middle of a fight or after I die or even while im walking around. It's not that the game stops working, its that it stops displaying new screens after these freezes start. I try to close it, but to do that I need to turn off my pc. By the time I get back, my team has either won, lost, or ff'ed. I've even got low prio que cuz of this. Thoughts?