I was having trouble with crazy freezing and distorted, skipping sound. So I erased and reinstalled the game. Now it freezes my entire system. There is no closing the client (ctl+alt+delete doesn't do anything) and restarting. Only hardstarting my comp instead. Please help, would love to know how to fix this.

Note: These problems occurred after I started playing again in October, hadn't been on since April. Comp security has LoL as an exception to make sure it isn't interfering.

I've had the same problem with my client, except it usually occurs when I'm about to respawn while I'm already in-game, or at the end of a game during the victory/defeat screen. This is not an issue with my internet connection, which I know for two reasons:
1.) I used to play problem-free on the same connection before I was "bugsplat" randomly one day
2.) My roommate plays on the same connection, and has never had the problem.
Also, for me, it's not an issue with my ping, which usually is around 80, but rather the FPS. Normally it runs at 60 FPS, but during the freezing and sound distortion it instantly drops to 1 FPS.
I sent my first support request on September 23, and RIOT tried to help me until October 8, when I stopped replying because the problem wasn't as persistent after following their advice. Now, however, the issue has come back with a vengeance.
To try to fix it, I've followed all of the recommendations that are listed on the website (https://support.leagueoflegends.com/...-improving-fps).
There was one additional step that the replied, which I was unable to perform. The support specialist sent a file titled "game.cfg" with which I was told to replace my existing file of the same name. I deleted the file that I already had, but then was unable to open the file that was sent, so I restored the old file that I had previously deleted. The error says that I'm unable to open it because "it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded)."
It would be greatly appreciated if this could finally be resolved, as it has caused me to lose on several occasions when it occurs during the game.