Freezing problem

I have a problem when i play league of legends. When i play and everything is good (or while i am at the loading screen) my game freezes and i can't do anything. i can't alt + f4, can't alt tab, can't use task manager, nothing. I am stuck at league of legends while it is frozen. So the only thing i can do is restart my pc (remember that all this happens while i am playing a rank game). So when i restart my pc and join to the game eveything is ok (except the fact that the game could freeze again). But i lose xp, farm etc in the game that end up losing not only my game, but the unlucky 4 people playing with me. This is so sad and i getting mad at it. I even end up 2 times as a leaver after the game, as if i wanted to leave.......

This doesn't have to do with my pc or anything, cause it also happens to 2 of my friends too

I also send riot a message but they didn't tell me anything neither anything was fixed............

So can anyone help me or dm riot about it?