You need to make xorg use the nvidia driver not nv, also try using the latest nvidia drivers. Using envy should sort that out (it has worked for me in the past).
Download the envy.deb from here ->
http://albertomilone.com/ubuntu/nvidia/scripts/legacy/envy_0.9.10-0ubuntu10_all.deband click the downloaded .deb file to install
Then from terminal run
sudo envy -t
hit 1 (I think) to install the nvidia driver.
If you can't get as far as the KDE desktop, then hit esc when prompted during boot and select to run the kernel in troubleshooting mode.
It will end up with a command line prompt, and type
wget http://albertomilone.com/ubuntu/nvidia/scripts/legacy/envy_0.9.10-0ubuntu10_all.deb
then
dpkg -i envy_0.9.10-0ubuntu10_all.deb
and run with
envy -t
(I haven't tried doing this in command line myself, but assume it will all work!)
It will probably be best to run the av wizard again after this so type
reboot
and hit shift on your keyboard after the first set of beeps on the kubuntu splash screen. You should here a different beep confirmation, and it will enter av wizard.
If you cant see anything after the av wizard start beeps then hit 1 on your keyboard. The av wizard will beep and restart with vga settings. If still nothing try 2, 3, 4.
Hope that helps