Seems you are having the same problem as I meet in Ubuntu 14.10 beta. I tried the latest driver from AMD website, latest in Ubuntu repo, none of them works. Drivers can be installed just fine, xorg.conf generated, but system can't boot. I can boot with radeon driver, or with fglrx-core installed. System boots fine with 14.04.
Seems you are having the same problem as I meet in Ubuntu 14.10 beta. I tried the latest driver from AMD website, latest in Ubuntu repo, none of them works. Drivers can be installed just fine, xorg.conf generated, but system can't boot. I can boot with radeon driver, or with fglrx-core installed. System boots fine with 14.04.