Boot into Ubuntu SAFE mode. When your GRUB menu appears on the screen at startup, choose the failsafe mode. This will boot you into Ubuntu in Run Level 3 (no X running). At the command line, restore your backed up xorg.conf or use this command:
Code:
$ dpkg-reconfigure xorg-xserver
to create a new xorg.conf.
What probably happened is that when you uninstalled the Nvidia drivers, the xorg.conf does not get modified, so it's still trying to load nvidia as the driver for X.
You can also just edit your current xorg.conf to use the driver nv instead of nvidia. This might get X to start for you.