I recently added a 2nd video card to my system, but unity refuses to extend my desktop over to the second screen. Although the secondary monitor initialises when I boot and I can move the mouse cursor over to the 2nd screen, the screen is otherwise blank (showing no wallpaper or interface elements) and I am unable to move any windows to this monitor.

Moving the mouse cursor over to the 2nd monitor changes it from the default cursor to the old-style X cursor, such as the one that appears when you run X-kill, indicating that this screen is initialised in the X Server but that Unity is not recognising it. Although the Nvidia X Server Settings application can see both monitors, the unity systems settings application does not detect the 2nd adapter. Sometimes the additional drivers application can see both adapters, but it doesn't consistently show options for them both. Xrandr also fails to detect the 2nd monitor, but iNex lists both adapters.

I have experimented with several different drivers for each adapter and with setting each of the graphics cards as the primary adapter in the BIOS, but this has made little difference.

The two adapters are an onboard Geforce 8200 and a PCIE Geforce 7200 GX. The onboard adapter is currently set as the primary, however this adapter crashes whenever I use the Nouveau driver and I have to switch over to the PCIE as a primary whenever I purge the proprietary drivers (switching back when the 304 driver has been reinstalled). It doesn't matter which adapter I set as my primary, the results are the same : one screen showing the unity interface and one screen showing an X-Screen that only displays the mouse cursor.

All I want is to be able to run this system in a dual screen configuration. I am not a gamer, nor do I require 3D rendering capabilities. Anything you can suggest to get the desktop to extend across both screens will be massively appreciated!