Ubuntu 12.04 changed itself to xubuntu and stopped working

[Nick Name]

Hi,

to get root access to your Ubuntu, you could boot a live media and assumed it's based on systemd, then systemd-nspawn or if it's not using systemd, then chroot.

However, it seems to be easier, if you still can boot into recovery mode.

Boot again into recovery mode, then run

mount -o remount,rw / && mount --all

FWIW sometimes odd packages install a desktop file in /usr/share/xsessions/, even if a WM or DE executed by this desktop file isn't installed.

Btw. did you make a typo?
plymouth -theme-xubuntu-logo 
       ^^^

Regards,
Ralf