change the entry in the file /etc/X11/default-display-manager I guess you have now /usr/bin/kdm and you probably need /usr/bin/gdm or something similar. Otherwise, you can also try the command: update-alternatives --config x-window-manager which allows you to choose the one of the available windowmanger and third, the file ~/.xsession can also have the entry of which windowmanger you want to use. cheers Pierre