I am running Ubuntu 11.10. I used the directions here to replace Unity with Gnome. It seemed to work fine until the end of step 2 when I rebooted the computer. When I chose the default option, I just got a black screen. When I choose the restore option and then "Restore normal boot" I get

Starting load fallback graphics devices    [fail]
Starting GNOME Display Manager [ok]
Starting Userspace bootsplash [ok]
Stopping GNOME Display Manager [ok]
Stopping Userspace bootsplash [ok]
Starting web server apach22    [fail]

(among a lot of OKs)

It finally gets to Stopping System V runlevel compatibility [ok] where it hangs. I left it overnight and just had a blank screen when I checked it in the morning.

I can "Drop to root shell prompt" and "Drop to root shell prompt with networking". I did see here that one should be able to fix the problem by choosing remount and then doing

apt-get install lightdm

I tried this as root shell with and without networking and got the message

Err http://us.archive.ubuntu.com/ubuntu/ oneric-updates/main lightdm i386 1.0.6-0ubuntu1.7
Could not resolve 'us.archive.ubuntu.com/ubuntu'

What is the best way to resolve this problem?

Thanks, Peter.