KDE does not start any more

["Hans-J. Ullrich" <hans.ullrich@loop.de>]

Dear list, 

since my last upgrade KDE4 is starting any more.
As I am starting KDE from KDM, KDE is starting, then the splash screen 
appears. After the third icon of the splash screen appears for millisecond, 
KDE is crashing, X is resetting and KDM is restarted.

Any other WM like LXDE, FVWM, XFCE and so on are working fine.

Where can I look? Which are the logfiles, where I should look? /var/log/syslog, 
/var/log/Xorg.0.log and /var/log/kdm.log did not help much.

I also created a new user, to get a fresh  ~/.kde, and I also tried another 
graphics driver (nv instead of nvidia).

My system is debian/testing, kernel 2.6.38-2-686 and the proprietrary nvidia 
driver (version 173xx-dkms).

Any ideas, how to have a clearer look, what is happening at start of KDE?

Thanks for the help!

Best regards

Hans