Game Drops to 0 FPS, Crashes/Disconnects, Makes Computer Slow Down During Incident

So ever since a patch or two ago, in random games (with increasing frequency, now it's every game) at a certain point (used to be past ten minutes or so, now from the time the game begins) I've been getting screen freezes that prevent movement or ability commands from going off until after the freeze. These freezes, in a given game, will increase in length, from about ten seconds in the beginning to several minutes later on, with only five to ten seconds between occurrences. Sometimes, it'll go away, and the rest of the game will be fine. Others, I'll essentially be disconnected for several minutes, while a burst of game sounds play during a frame change every thirty seconds or so. Closing the game and reconnecting used to help, but it's not viable since the screen freeze also prevents me from performing other tasks (Control-Alt-Deleting takes much longer between command and the screen popping up, as does loading up Task Manager, and Alt-F4 doesn't seem to work at all) and, recently, even reconnecting does not get rid of the issues. I noticed a while into having these problems that immediately after the freeze ends, or just moves to another frozen frame, the FPS counter is at 0. I typically get 80 FPS or so in a game normally, at 14 ms. I've been playing for over a year and a half now and never ran into these issues until in the past month or so.

So far, by the advice to similar issues and on my own accord, I have:

1. Restored the default settings of my graphics drivers
2. Updated said graphics drivers
3. Ran a full repair on League of Legends
4. Defragmented my hard disk
5. Started playing without other tabs open (Chrome especially)
6. Closed background tasks in Task Manager before playing, including Steam and Discord
7. Ran an antivirus check
8. Went through and cleaned out a metric ton of programs and files I no longer use on my PC
9. Lowered the graphics settings to very low

I have played matches after each of these steps, and the issue persists. As of recent times, it's intensified. No other game on my PC has issues, just League. I need this to be fixed. I am literally losing my friends games because I win lane for ten minutes, then sit there, get killed, and don't come back because my screen is frozen, and every so often a burst of sound will come on with the sounds of me taking damage and dying, then my tower dying, etc. League is unplayable in this state for me. I'm tempted to do a full reinstall, but I fear I'll just be met with the same issues. Please help me find an expedient solution, or fix the game so I can play.