I faced the same Quantal to Raring upgrade problem on Ubuntu 12.04 LTS with Hardware Enablement as reported here.
In order to get it to work, I had to remove Xorg for Quantal then upgrade everything to Raring. I did this from the command line terminal:
$ service lightdm stop
$ apt-get autoremove xserver-xorg-lts-quantal
$ apt-get --install-recommends install linux-generic-lts-raring xserver-xorg-lts-raring libgl1-mesa-glx-lts-raring
$ apt-get install linux-tools-lts-raring
That was it. Upgraded to LTS-Raring hardware enablement kernel and Xorg.
PS: The only issue with this upgrade was that I lost back-light control on my XPS13 laptop as reported here.