Comment 4 for bug 140922

Yep, your workaround finally lets GNOME start on my screen. Thanks! Here's the complete How-To for those who might have the same problem:

1) Start your Live-CD and press F6 (Further Options)
2) Delete the commands splash and quiet (they're at the end of the line)
3) Replace them with "break=bottom" (without the quotation marks), Press ENTER
4) Let the Live-CD boot up to a command saying "(initramfs)" (booting might take a while!)
5) now enter "chroot /root" (without the quotation marks) next to (intramfs), Press ENTER
6) enter "sudo nano /etc/X11/xorg.conf" (might work without sudo too), Press ENTER
7) scroll down to Section "Monitor" and add an extra line: Option "MonitorLayout" "LVDS, NONE" (with quot. marks)
8) press ctrl+o to save, then exit with ctrl+x
9) enter exit to leave chroot /root, Press ENTER
10) enter exit again to leave initramfs, Press ENTER
11) drivers should load automatically now and GNOME display manger (or KDE) should start on your screen

I hope I could remember everything right and it helps those with same problem (the issue seems to be that ubuntu sends the GDM signal through the wrong line - the one going to a second monitor - and not to the connected screen; LVDS, none activates dual screen support so that a graphics signal is sent through both lines)

I had exactly the same problem with Edgy, it was gone with Feisty but Gutsy seems to have brought it up again. Hope this changes in upcoming releases! :-)