I recently updated to the 3.13 kernel on Fedora Core 20 and the 12.1 ATI drivers stopped working. I fixed this by downloading the 14.1 beta drivers which support that kernel. Download this here: http://support.amd.com/en-us/kb-articles/Pages/Latest-LINUX-Beta-Driver.aspx. This works perfectly for those Fedora 20 users like me who are also affected by this update. Just uninstall the old drivers using this command.
Then run the installer for the latest drivers downloaded from the above link. This really works.
unzip amd-catalyst-14.1-betav1.3-linux-x86.x86_64.zip chmod +x amd-driver-installer-13.35.1005-x86.x86_64.run ./amd-driver-installer-13.35.1005-x86.x86_64.run
Then restart your system.
Then you will have a working accelerated Linux desktop again!