My hard drive got full yesterday and some weird things started to happen, like uGet not working anymore and the trash can not emptying. I switched to another OS and cleaned some stuff in the Xubuntu's partition. However, when I restarted the computer, the login GUI changed to this and I can't fix it. Does anyone know how to get back the original xfce interface? Ugly login GUI image
I don't konow which displaymanager Xubuntu uses normaly. But you can run the comand to reconfigure your Display manager:
sudo dpkg-reconfigure lightdm
If it is missing try to install it:
sudo apt install lightdm
lightdm you can also use
gdm3 wich is the default for Ubuntu (Gnome).