OK, that xorg.conf is missing a lot of sections .. If I were you I'd follow the instructions in section 2.1 here:
to uninstall,reboot, install, configure, reboot, and test the drivers.
Any questions .. feel free to ask before you attempt this.
The important part (after reinstalling the drivers) is to run:
sudo aticonfig --adapter=all --initial
sudo amdconfig --adapter=all --initial
BEFORE rebooting .. which should generate a FULL working xorg.conf