Solved by Mona_Jalal in post #4 
              
              
                I followed these exact instructions and now it works: 
sudo apt purge '^.*nvidia*'
sudo apt install ubuntu-desktop
sudo apt purge "^.*cublas*"
sudo apt purge "^.*cuda*"
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.old
sudo apt autoremove
sudo reboot now

While rebooting, disable Secure Boot and let…