I had the same exact problem when I did a fresh install of 12.04 and 12.10. You can give these troubleshooting steps a try, hopefully it is not too late.
The first step is to boot with "nomodeset" enabled in the kernel options.
Open the link below and scroll down to the section that reads, "How to temporarily set kernel boot options on an installed OS." Once all steps are completed and you should be able to boot into a functioning desktop.
The next step requires you to install the respective nvidia driver. To do so I recommend that you run the following commands:
Next you can use one of the two following commands. One is for nvidia-current and the other is for the nvidia-current-updates. I don't know much about the difference betwen the drivers. I do recollect reading that nvidia-current driver is more stable, while the nvidia-current-updates run on a more bleeding edge.
sudo apt-add-repository ppa:ubuntu-x-swat/x-updates
sudo apt-get update
sudo apt-get install nvidia-current
Once you reboot (fingers crossed), you should be back up and running ...
sudo apt-get install nvidia-current-updates