I installed a new Raedon R9 290X after upgrading from my old Nvidia GTX 570, installed the AMD Catalyst 14.6 drivers and everything booted fine but games where a little laggy. I decided to remove the old Nvidia drivers by running
sudo apt-get remove --purge nvidia-*
After this I could no longer boot as it can no longer detect my display drivers and won't even enter "low graphics mode", although the screen to allow the option appears. Viewing the config files return nothing, the files are empty according to the screen. I can still access the terminal.