Take a look at
this Ubuntu thread Read it carefully, especially Tuxcantflys posts. You have Kubuntu, so take note of the gdm vs. kdm starts of the gui.
The last post suggestions should work getting into gedit and changing the nvidia entry to nv or vesa.
anyhow, use sudo /etc/init.d/gdm start
as for the fallback drivers, do this:
sudo gedit /etc/X11/xorg.conf
find the line that says "nvidia" under the section "device"
change it to "nv"
then do sudo /etc/init.d/gdm start
Hopefully this will get it going.