I have Ubuntu 14.04 and a XFX Radeon HD 7970.
My system was running fine but after the last upgrade (26 September 2014), I'm not able to restart. The system is loading (I can see part of a Teamviewer window which is a program opening at the start of the system).
The rest of the screen is black and I have a cross cursor. I have access to the command line with Ctrl+Alt+F1.