All dm's failing

[Carlos Kosloff]

After the botched upgrade involving libqt5x11extras5, my computer cannot 
start normally.
The latest upgrades brought newer versions of sddm and 
glx-alternative-*, which are now at 0.6.93.
sddm is also in the video group, in spite of all that sddm does not work
I purged and reinstalled kdm, no luck, it is broken with following error:
Cannot load /usr/share/kde4/apps/kdm/faces/.default.face: No such file 
or directory
lightdm does not work either.
I am out of ideas.
Can somebody help?