I have a vaio laptop with an ATI Radeon video card and an external screen.
I used to run dual monitors on Ubuntu 10.10 fine, but recently decided to upgrade to 11.10 via 11.04
I don't think it's the video card or the fglrx driver. It seems to be unity.
When I start up, the laptop screen is normal and the external screen is all white, although I can move my mouse over it. However, the cursor becomes the big X that used to be cursor of the first versions of Xwindows.
I can right click on it, and it brings up the context menu for the desktop. And then, all of a sudden, it shows my desktop background.
I can continue to move my mouse over the external screen, and now the cursor is normal (little white arrow).
But I can't do anything any longer (not even the context menu as before), and trying to drag a window to it (which always worked on 10.10) doesn't work.
I actually really like unity. It gives me the most our of my desktop, and uses all space available, which is great. But how can I get my second screen back?
I tried unity 2D, but the result is the same.
Edit: I think I stumbled on this bug: https://bugs.launchpad.net/ubuntu/+source/nvidia-settings/+bug/882143