GUI in Linux Mint won't load

Using Linux Mint 20 (Ulyana), which was working fine yesterday. The GUI seems dead. I get icons, a black screen. I managed to get cinnamon up using the terminal, but if I close the terminal it's gone: no menu, no panels, nothing.

I have tried ...

a. replacing the .cinnamon directory from a backup
b. changing back from modern to traditional panel
c. Installing a new LM20 from the DVD, without overwriting /home

The only way I get a usable LM is by using the Terminal and typing the command Quote:

cinnamon

I'm completely baffled.

Cecilieaux