I've had the same issue with Ubuntu and gave up. I still run windows for my dual card systems.
Does anyone know how to fool a second video card into activating without plugging a monitor into it? If so, I'll go back and try again.
Dummy plugs and/or monitors are not required for Linux. I believe the issue here is installing a 2nd card after the initial installation of Ubuntu.
I had the same problem above when I installed a 3rd card to Linux. I have since fixed the problem by using the above fix, but adding SUDO.
"sudo aticonfig --initial -f --adapter=all"
"sudo reboot"
This has fixed the problem and everything is working great.