I have installed these AMD drivers for my HD 5770: http://support.amd.com/us/gpudownload/linux/Pages/radeon_linux.aspx
When I launched Steam it threw me an error that something was wrong with OpenGL, told me that performance may suffer and let me proceed. After that I attempted to download CSS, but because it was slow and didn't exit I force killed the "steam" process. After I reboot the PC I get the login screen, which I can log in from but when logged-in I get no Unity, no Dashboard etc etc. Only my desktop background, the mouse pointer. I suspect the problem may be with the drivers displayed above, how could I remove those drivers?
EDIT: When I boot to guest mode (I can't bring up the terminal on normal account because of different layout) and launch CCSM it tells me when I enable the Unity plugin that it needs to also enable OpenGL(asks me that twice) and some other plugins.
EDIT 2: Whenever I try sudo apt-get purge fglrx I get told that the package does not exist.
I've tried the answers here but none of these help.