SERIOUS issue

Ok so... I used to have 0 issues with my computer. Ever since I restarted it, it has been almost impossible to play a full game of League. My computer freezes constantly (even just using boards), never loads a game, and often gets me AFK reports. Just now, I almost got leaverbuster because my computer froze when the match was found. I also almost got kicked form a lobby because it froze until 6 second remained to ban. Then, it froze about 7 times while loading and stuck at 100%, never letting me in. My team remade. I can no longer play this game, it seems.