I recently installed a different kernel on Linux Mint 14 and my ATI drivers were not working. To fix this I had to install the kernel headers for the appropriate kernel that I was running.
john@adeptus-mechanicus ~ $ sudo apt-get install linux-headers-3.5.0-25-lowlatency
Then I could navigate to the directory containing the ATI drivers source.
john@adeptus-mechanicus ~ $ cd /usr/src/fglrx-9.000/
And then run the make.sh script to re-build and install the kernel modules.
john@adeptus-mechanicus ~ $ sudo sh ./make.sh
This re-built the ATI fglrx drivers and installed the kernel modules. Then I loaded the kernel module into memory thusly.
john@adeptus-mechanicus ~ $ sudo modprobe fglrx
Then I logged out of my Cinnamon session and the GDM login manager loaded with the enhanced Gnome Shell login; showing that the drivers were working. This is how easy it is to re-install the ATI drivers, but you need to ensure that your kernel package has the properly configured kernel headers to build against.