I've recently updated to 14.3 beta on Ubuntu 14.04, with a R9 270, and xorg is not starting up.
I'm far from home now, but as soon as I get there, I will try fallback graphics again to get the logs and post here. Is anyone having the same issue?
First, before installation of new Catalyst drivers make sure that You have installed these packages:
sudo apt-get install -y build-essential cdbs dh-make dkms execstack dh-modaliases linux-headers-generic fakeroot libqtgui4 lib32gcc1
If You need more information on uninstall/install instructions, just ask.