I have just had a strange experience: I installed Debian 6, choosing KDE as my desktop on an hp Z400 with an NVIDIA graphics card - this works fine after I have added the proprietary driver. The strange thing is, I then edited kdmrc - both /etc/kde4/kdm/kdmrc and /var/run/kdm/kdmrc - first to allow root to log in (I know all the arguments against, but ... basically, this is my machine, so I decide), and then a second time to get it to display the analogue clock.

The first edit went well, except when I tried to start kdm with "/etc/init.d/kdm start". it didn't come up, but it did when I rebooted; that is the first strangeness. The second time it stopped working completely; I could see kdm in the process list, but no X and no greeter - and of course, no desktop.

I have got things back by purging and reinstalling kdm, but why a couple of simple edits of the config file break things so completely? Any ideas?

It is probable that you broke the format of the file somehow, causing KDM to no longer be able to start. Error messages relating to KDM startup can usually be found somewhere under /var/log/

bcooksley - thank you for replying. I'll keep an eye out for that, but so far it seems to be OK after I reinstalled.