Entire Project Stopped Working (tons of compile errors on scripts)

Hi,

I'm a bit of a newbie when it comes to this whole thing but I'm pretty sure this shouldn't happen. My project was working completely fine and then one day when I started up my unity editor (version 2019.4.14f) suddenly there were tonnes of compile errors on the scripts that were working just fine before and most of these confuse me since I can't find any way to fix them (in fact, some of them were in the editor's own scripts!).

I've attached screenshots of some of the errors.



Thank you!

 

This seems to be causing alot of issues.

 

This as well.