League causes my computer to crash ever since 5.6 update

I can load and log onto league just fine, but when I'm in a game, usually about the 20 min mark, my computer freezes and I have to hard reset my computer. I know for sure it isn't my computer and It wasn't a problem until just recently. It is making me frustrated and if the problem persists, I may just stop playing league, however, I would rather just find out what the problem is. I have read on some of the other discussions problems similar to mine, but I haven't interpreted theirs as the same problem.

While I'm in game, the first 20 or so minutes are fine. Then my computer just freezes, my screens say they have lost connection to the computer, and the sound is just a repeat of what happened in the half a sec before it froze. I have un-installed and then re-installed league and it didn't help at all. I am not on a laptop, and my computer only does this when I'm in a game. I have tried to repair league as well. Assistance would be greatly appreciated.