Upon activation of the 3d graphics card freezes ubuntu 3d, in all versions. only in gnome classic without any effects, it is possible to enter. Compiz does not work in ubuntu, if you not turn the graphics card on by using this command "sudo usermod-a-G video username" ubuntu work well only without 3d effects. But if you want to try compiz you can always try debian or mint which both supports radeon graphics card and compiz. But Ubuntu is a nice OS which I would recommend you look at, but without turning off the graphics card to
