After a recent adventure with Linux Mint Debian I had to reinstall my ATI graphics drivers. A simple process;
These instructions will install ATI graphics drivers from the repositories for Debian and Linux Mint Debian. These should work for other debian based system however they have more than likely configured your graphics drivers for you.
Open up your core repositories to have main contrib non-free.
Either su into root or use sudo and install with
apt-get install fglrx-driver fglrx-control
Then set up with
Reboot and confirm everything is working with