i had the same problem in ubuntu 18.04 after upgrading to nvidia-drivers-390.48, than i could not login even using nouveau after removing all nvidia driver.
GDM3 could not manage to boot properly but just installing lightdm and setting it to default let me login successfully (i did not remove gdm so it was not necessary to do so to fix it)
i had the same problem in ubuntu 18.04 after upgrading to nvidia- drivers- 390.48, than i could not login even using nouveau after removing all nvidia driver.
GDM3 could not manage to boot properly but just installing lightdm and setting it to default let me login successfully (i did not remove gdm so it was not necessary to do so to fix it)