I work with machines that use Llano CPUs with the integrated graphics chip (in this case the A4-3400 primarily), and have repeatedly run into a problem with graphics drivers. Trying to load a Ubuntu live CD will only give a black screen, with the system unusable. The only way so far I have managed to get this to work is by applying the 'nomodeset' kernel parameter during boot, which gives a display but at horribly low and distorted resolutions.
In these machines, the video output is provided using the VGA connector, not DVI or HDMI. I found a bug detailing my problem: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/943263, but with the last posts back in 2012 I can't help but think something must have changed.
Installing Catalyst (fglrx) does work, but it is not a solution due to the manual intervention required on every affected machine (think 40+ machines). For the same reason just using nomodeset is not a solution.
I have tried using the latest xserver-xorg and xserver-xorg-video-ati on Precise, along with the Raring backports (xserver-xorg-lts-raring and xserver-xorg-video-ati-lts-raring respectively) with the dependent kernel versions (3.2.0 for the stock Xorg and 3.8.0 for the backports) but to no avail.