8th April 2017, 19:03
If you figure out what went wrong you can fix it.
So from the login screen you could reach a terminal (tty) by pressing ctrl+alt+f1 for example and login there.
From there you can take a look at the .xsession-errors file and see if it lists any error at the end which has something todo with why it does not start the desktop for you.
You could also check if plasma-desktop and plasma-desktop-data packages are really installed.
Though it would be strange that it worked before and suddenly does not.
Did you perform any other installs or removal that you can revert?
So from the login screen you could reach a terminal (tty) by pressing ctrl+alt+f1 for example and login there.
From there you can take a look at the .xsession-errors file and see if it lists any error at the end which has something todo with why it does not start the desktop for you.
You could also check if plasma-desktop and plasma-desktop-data packages are really installed.
Though it would be strange that it worked before and suddenly does not.
Did you perform any other installs or removal that you can revert?