After entering the password — black screen (ubuntu 18). How to turn on the screen or system restore?

Alt+ctrl+f2
There smiling the terminal, where you enter in your user and restart your window Manager in Ubuntu 18 default gnome+lightdm, here is the link to the gnome
. Also check and change the resolutionhttps://askubuntu.com/questions/455301/how-to-rest... and LDM restart sudo service lightdm restart
If nothing works, then remove using apt purge, and put again, do not forget to remove or rename directories .gnome and .gnome2: /home/ or put another, for example unity
Don't know what the Manager? Just put and run another. Everything Google on the Internet.