I just upgraded from 9.10 to 10.4 on my Dell Latitude E6500.
The laptop sits in a docking station.
In 9.10 I would use Fn-F8 to switch to the external monitor. With 9.10 I did not have to do anything special to allow this switching to occur.
After upgrading I can no longer use Fn-F8 to switch to the external monitor.
Anyone have any ideas or can suggest what additional information I can provide to disgnose teh problem?