No users can log on to X, suddenly !?

[Uwe Dippel <udippel@uniten.edu.my>]

As of today, I found that the only logon with X is possible to root.
Any other user will simply get back kdm, whatever he / she types.

I created a new user to test it: just the same: kdm-applet keeps coming
back forever. No indication of 'wrong password' or so.
The only session working however, is 'Failsave'.

For root there is no problem.

Users *can* log on to Console, though. But then X would not start; without obvious error message. 
Root *can* startx, though, without problem.

Stumped, again !

Uwe