I tried all methods presented by the generous members of this list, but with no good fortune. I hope someone will find it useful.
Use a Ubuntu live distribution CD to reach a command-line terminal. First check that your $HOME directory (/home/username) has appropriate permissions, and that all directories can be examined with the "ls" command.
Then useand remove any nautilus files and folders which might remain in $HOME. Also remove .ICEauthority from /var/lib/gdm (if it exists). Then you can reboot withCode:sudo apt-get remove nautilusand on restart, get to the CLI and useCode:sudo shutdown -r nowand remove the CD from its drive. On reboot, I can only hope that you have the same luck as me, and arrive safely at your usual login form.Code:sudo apt-get install nautilus sudo shutdown -r now
Thanks to all, and best wishes,