[client]no sound in game, random fps drop, freeze when trying to exit game

So I was playing a ranked game, when I got into champ select I realized there was no sound effect. I didn't think too much into it and I went into the game, then suddenly I realized my fps was dropping super hard ranged from 4~11, my usual fps was usually over 40 so it seemed very weird. I tab-alt out of the client to check task manager, and nothing other than league was running, so it shouldn't be the computer's problem but the client bugged. So I tried to exit the game to reconnect, but the screen froze and nothing happened. I waited for like 3 minutes and still nothing happened. I couldn't even alt-tab and pressing any key on the keyboard have no effect(even ctrl-alt-del). I realized it was some serious shit happening and I force shutted down my computer, and it took like 5 minutes for it to restart. Then I logged back into the game and everything was normal, except the fact that I was afk since lv4 and now everyone is lv15+ and my team lost the lead we had.

I wonder if there is something wrong of the client because this had never happened to me previously. And I am very worried that this might happen again.