After enabling the nvidia prop driver, kubuntu seems unable to start a graphical session. I thought I'd be able to do a console login using alt+ctrl+f1 but although I get to the console screen with the end of the boot messages with a login prompt, none of the logins I've defined seem to be accepted. the login prompt comes back without the chance to enter a password.

Any idea ?

Welcome to Linux Questions.

1) Login to "Recovery mode" (line 2 in grub)

2) You will come to a "Recovery Menu" , please
choose (5) root .. "Drop to root shell promtpt"
.. then <Enter>

You can now edit /etc/X11/xorg.conf or hopefully
use the xorg.conf.backup if you have it, or run
'dexconf' to make a basic xorg.conf .

Good luck !

Just curious, did you try to use Envy?

IGF

Why not ? After stopping to use Linux for such a long time, I stupidly assumed that tools provided in a release version could be trusted but seems there has not been so much progress on that front.
I knew nothing about Envy and had used automatic nvidia driver utilities in Suse in the past.

The annoying surprise was the stripped down xorg.conf.

knudfl, I'm not able to do that because I was using a manual lilo boot (because of problems with grub) and I didn't have a failsafe option.

Will reinstall tonight with a small boot partition at the beginning of the drive so that I can use grub.

Reminds me why I stopped using linux a while back : so time consuming !