Unity - NO LICENSE all of a sudden

I have been using Unity on a PC (personal development) since around May this year. It has been fine. I have two projects being developed using 2019.3.14f1.

All of a sudden, when I try to load a project from the unity hub is says "error launching editor: license is invalid - Manage license". I click manage license, and it says - no license, either activate a new license, or manually activate.

I try activate a new license, select personal / not professional capacity, and it says Your License successfully activated", followed a second or two later by "Machine identification is invalid for current license".

Still cannot open a project. Try it again. No good.

So I try manual activation. I click save license request, and go to the manual activation page. I browse to and upload the license. I click personal edition / not professional capacity. I download Unity_v2017.x.ulf. I then load that licence file to the Manual activation dialog and confirm.

It says "invalid license file".

I am now completely stuck, cannot access any project. What do I do now to get it going again?

The only thing that has happened is that the display driver (NVidia) got corrupted and had to be reinstalled. Other than that the PC is unchanged and there have been no Windows updates since it was last working.