No playback whatsoever, though play button turns to stop button

I'm on Windows 7. This started on version 2015.3. Everything was working fine, then I moved the playhead back a few seconds to watch an edit I just made and when I hit space to play the timeline did not play. I've also tried clicking the play button. I've also tried jogging with J, K, and L. None of these commands do anything. I've encountered this problem before for years now, through many different computers/operating systems/premiere versions/etc. I've usually been able to solve this by either changing the playback quality back (either up or down), restarting premiere, sometimes restarting the computer, or closing out the sequence and re-opening it.

Today none of that worked. Today I also tried:

- Updating to the latest version of premiere (From 2015.3 to 2017)

- Trying older builds

- Turning off and even completely removing anti-virus

- Cleaning and deleting cache

- Changing cache destination

- Updating my GPU driver

- Restarting my computer after every one of these steps

- Changing audio playback settings (arbitrarily trying combinations)

- Changing video playback settings (arbitrarily trying combinations)

- Copying and pasting sequence into a new project

And the problem is with every project I open. The problem isn't just with the timeline, it's all playback in general. Also an interesting note is that when I want to close Premiere, whether I want to X it out or click File>Quit, the project closes, but Premiere stays open with a large empty gray screen with the toolbar at the top. From there I can click X or File>Quit AGAIN to close it. I've waited minutes for it to close on it's own, but it won't-- so the second click is needed.

Any suggestions?