Screen frozen and game crashing

Today when I'm playing Leblanc, at the beginning of the game, when I was warding the bush, my screen suddenly froze. Like, I can't do anything to it, I can't even exit league. So all I did was shut down the computer and restart it. When I enter again I'm underfarmed and we lose that game bc the enemy midland was so fed. Thankfully this is a normal draft and not a rank, or I woulda be SO tilted. Also the game crashes 3 times during one of my Syndra games. Riot plz fix.