We have been able to replicate the issue, and have confirmed that the issue is with the ATI proprietary drivers. Gnome Shell is incompatible with the ATI proprietary drivers, and trying to remove the drivers does not completely remove them, preventing use of any 3D accelerated environment. You can properly remove them using these commands run at a terminal:
This will properly remove the drivers and allow you to run Gnome Shell.
sudo /usr/share/ati/fglrx-uninstall.sh #This one may not work; if not, that's okay.
sudo apt-get remove --purge fglrx
sudo apt-get remove --purge xserver-xorg-video-ati xserver-xorg- video-radeon
sudo apt-get install xserver-xorg-video-ati
sudo apt-get install --reinstall libgl1-mesa-glx:i386 libgl1-mesa-glx:amd64 libgl1-mesa-dri:i386 libgl1-mesa-dri:amd64 xserver-xorg-core
sudo dpkg-reconfigure xserver-xorg