Macbook air super laggy, now Sound buttons don't work

[pjk]

Here are the specs of my laptop:

https://www.dropbox.com/s/gblg9u5c3la34l6/Screenshot 2019-03-05 17.58.58.png?dl=0

Last night my laptop worked great and has worked great for over a year with no issues. Today when I was working it was super laggy, and almost out of disk space (2GB left or so), so I removed 15GB+ of files. I deleted the VPN I had (that was freezing), then I installed a security update that has been needed, and immediately upgraded to Mojave.

Since the upgrade finished, the sound button doesn't work (shows a circle with a line through it when pressed), and when I open any Youtube or window, it lags a lot. I never had this problem before.

I shut down and reset PRAM with the alt+command+P+R, and no change.

When I go to System Preferences > Sound, I get (after a laggy 5 second wait):
"could not load Sound preferences pane"

So overall the computer is super laggy, but the sound is one thing that is obvious that may be related. Any ideas what I can do to solve this? I've tried all the main stuff I could find online, but still having issues. Any other suggestions would be much appreciated.

Thanks.

 

[Audit13]

Have you tried erasing and reinstalling Mojave?

If it possible the unit was exposed to liquid?

Possible loose internal connection?

 

[pjk]

Have you tried erasing and reinstalling Mojave?

If it possible the unit was exposed to liquid?

Possible loose internal connection?

I restored to a couple weeks prior and it solved the issues. Will avoid upgrading for now. No liquid issues or internal connections afaik. Thanks.