ubuntu I only start with startx
ubuntu 18.04 freezes purple screen in login

https://itsfoss.com/switch-gdm-and-lightdm-in-ubuntu-14-04/
https://www.enmimaquinafunciona.com/pregunta/130871/que-es-gdm3-kdm-lightdm-como-instalarlos-y-eliminarlos
https://askubuntu.com/questions/264532/revert-back-to-nouveau-drivers

https://askubuntu.com/questions/223501/ubuntu-gets-stuck-in-a-login-loop
https://askubuntu.com/questions/223501/ubuntu-gets-stuck-in-a-login-loop

**POSIBLES SOLUCIONES**
1. PERMISOS
ls -lA ~ | grep .Xauthority
chown neverkas:neverkas .Xauthority
ls -lA ~ | grep .ICEauthority
chown neverkas:neverkas .ICEauthority

2. REVISAR LOGS Y PROFILE
sudo gedit /var/log/Xorg.0.log
sudo gedit ~/.xsession-errors
sudo gedit ~/.profile

3. Instalar && Reconfigurar los paquetes de GDM3
# sudo apt-get install gdm3
sudo dpkg-reconfigure gdm3
sudo service gdm3 restart
sudo dpkg --configure -a ; este nose q hace..

4. Agregar un nuevo usuario para ver si accede
sudo adduser testing --group sudo

5. Revisar si funciona GDM3
systemctl status gdm3

6. Actualizar kernel y paquetes
sudo apt-get update
sudo apt-get dist-upgrade

7. mover la configuración XORG
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup

Is your HOME your HOME?

    Check the owner of your home directory using ls -l /home
    If you don not own your home directory, change it using sudo chown $USER:$USER $HOME
    Try a restart using systemctl reboot -i and hope your login loop is fixed.

Do you own your .Xauthority?

    Check the owner of your home directory using ls -l ~/.Xauthority
    If you don't own your .Xauthority, change it using sudo chown $USER:$USER ~/.Xauthority
    If you do, move your .Xauthority file using sudo mv ~/.Xauthority ~/.Xauthority.bak
    Try a restart using systemctl reboot -i and hope your login loop is fixed.
    You might need to do the same thing on .ICEauthority.

Is your /tmp right?

    Run ls -ld /tmp and make sure the permissions are exactly drwxrwxrwt. The output should be of this sort

drwxrwxrwt 27 root root 36864 Sep 17 17:15 /tmp

    If not, run sudo chmod a+wt /tmp
    Try a restart using systemctl reboot -i and hope your login loop is fixed.

Maybe lightdm is your problem?

    Reconfigure your display manager using dpkg-reconfigure lightdm and try out other display managers (gdm3,lightdm,) that are available. Maybe this will you give you enough clues to move forward.
    If none of them help,try installing sddm using sudo apt-get install sddm
    for one final try. reconfigure display to sddm.

If none of the above solutions worked, you can try re-installing ubuntu.