Since upgrading to Ubuntu 19.10, I've had the issue that Ubuntu would just get stuck before or after the login screen.
After some searching I found the recommendation to remove
quiet splash from the grub options, and indeed that fixes the issue for me!
Specifically, at the stuck login screen, change to a terminal by pressing e.g.
ctrl+alt+f4, login, then run
sudo nano /etc/default/grub to edit the configuration for grub (the bootloader). Find the line that says
and change it to
save the file, then run
sudo update-grub to apply the changes. Reboot (by running
reboot or pressing
ctrl+alt+delete), then you should be able to login again.
You may have to repeat this after some system updates (even though they are supposed to prompt you before overwriting your config).