Unity can't see any scripts

One day I booted up Unity, and all my script components on every object had this error under them:

The associated script can not be loaded. Please fix any compile errors and assign a valid script

The scripts had all been working for weeks before this. This error appears to have popped up for no reason.

The component still sees the script, it knows that it's there, but it can't load it.

And when I try to add a new script component, the menu that normally lists all of the scripts in the project's various folders is empty. Here's a screenshot.

I've tried making a new project, and the same problem occurs. I've also tried reinstalling Unity and creating new scripts with the same contents but a different name and adding those. Nothing. Any ideas would be super appreciated.