I recently updated to a new kernel version and the ATI drivers were not loaded as they had not been built for that kernel. I had to re-compile the ATI drivers, so I switched to the root user and navigated to this folder.
[root@localhost homer]# cd /lib/modules/fglrx/build_mod/
Then I ran this command to build the kernel modules.
[root@localhost build_mod]# ./make.sh
Once the compilation was done I had to then navigate to another folder to complete the build.
[root@localhost ~]# cd /lib/modules/fglrx/
Then run the ./make_install.sh script to complete the installation.
[root@localhost ~]# ./make_install.sh
Once the driver installation has succeeded, logout and then log back in to the graphical environment. This is all I had to do to get my accelerated desktop working again.