oula... Bon je ne connais pas trop KDE mais je pense que si tu n'a pas de xorg.conf... tu as un soucis !
Perso je testerai de créer un xorg.conf et d'ecire ceci a l'interieur :
# /etc/X11/xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the /etc/X11/xorg.conf manual page.
# (Type "man /etc/X11/xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
# sudo dpkg-reconfigure -phigh xserver-xorg
Section "Device"
Identifier "Carte"
Driver "vesa" ## nv pour les NVIDIA (libre), ati pour les ATI (libre).
BusID "PCI:1:0:0"
EndSection
Section "Monitor"
Identifier "Moniteur"
EndSection
Section "Screen"
Identifier "Ecran"
Device "Carte"
Monitor "Moniteur"
DefaultDepth 24
SubSection "Display"
Depth 16
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 24
Modes "1024x768" "800x600" "640x480"
EndSubSection
EndSection
Ensuite tu tape
sudo /etc/init.d/kdm restart
Teste ca... mais je promet rien
Tu peut egalement faire un file system check au cas ou mais bon...
fsck
