I have same problem. After dist-upgrade from 17.10 to 18.04. I get black screen, and tty only.
I can startx after removing nvidia
sudo apt-get purge nvidia*
sudo apt dist-upgrade
and remove old xorg.conf
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf_bck
Now I can get X with startx, but on boot I still getting only black screen and tty.
I have same problem. After dist-upgrade from 17.10 to 18.04. I get black screen, and tty only.
I can startx after removing nvidia
sudo apt-get purge nvidia*
sudo apt dist-upgrade
and remove old xorg.conf
sudo mv /etc/X11/xorg.conf /etc/X11/ xorg.conf_ bck
Now I can get X with startx, but on boot I still getting only black screen and tty.