Problem

After apparant successful graphical login, I return at the login prompt.

Solution

Removed erroneous line from ~/.xinitrc:

xmodmap .Xmodmap

Erroneous, because the file .Xmodmap didn't exist.

Look in .xsession-errors for login errors.

Console login (CTRL-N) used to work, but now it doesn't work either.

Following lines are in .xsession-errors:

/usr/X11R6/bin/xmodmap:  unable to open file '/home/freddy/.Xmodmap' for reading
/usr/X11R6/bin/xmodmap:  1 error encountered, aborting.