Game Crash

So basically, for the past week, my client has kept on crashing every five or so games. This happens most often in ranked games, though I do not know why. My game freezes and then my computer does too, then I can't do anything and have to restart my computer by holding the restart button. After it restarts, it starts to patch and scan my files, fixing the game. This process takes about an hour, and I can't connect to my current game. I have been gaining leaver buster because of this from the past week, and its been nagging me really hard. I had a game where I went flawless 10 cs per minute and 8 kills as Darius, but then I crashed. We still won that game because their team was behind, but I couldn't reconnect so I was given a leaver buster. Please help! [zombie-nunu-tears]