How can I get past the blank purple screen on my Ubuntu 18.04 LTS system?

[マスターズ・イアン]

Folks & Little Girl
Finally had half an hour to try some of Little Girl's suggestions.

On this page:
https://askubuntu.com/questions/1050672/gdm3-does-not-start-in-ubuntu-18-04/1079363#1079363
1. Editing /etc/gdm3/custom.conf and uncommenting "WaylandEnable=false"
Rebooted. No change. Still a lovely purple screen.

2. Same page, someone suggested:
sudo apt-get install lightdm
sudo dpkg-reconfigure lightdm
Rebooted, now I have a usable desktop again!

So at some point GDM crapped out and by re-installing lightdm the problem got fixed.

Thanks Little Girl and everyone else that made suggestions!

ian