Go back to the OS that worked for now. Ask the machine's makers when the drivers will be ready.
If no one told you, Windows 8 is new and just like the last time it can take a year or 2 for drivers and support to arrive.
I am running Windows 8 and have two monitors and a graphic tablet connected to a NVidia GeForce GTX 590 Card. On previous versions of Windows it was easy to switch between my second monitor and tablet but since upgrading to Windows 8 I don't get an image on the second monitor. What is strange is that I can see the mouse pointer!!
I have tried making the 2nd monitor the 'main monitor' but then I don't have an image on any display. When I swap the connectors round, I do get an 'extended display' but it behaves strangely. When I click 'Identify', my main monitor is shown as number 1 though the second one behaves as such (that is the one I set as the 'Main Display' before swapping the leads round).
Running a program launches in the second monitor. If I swap the leads back round, I only get an image on my main monitor and the mouse cursor in the second.
The same thing happens with the graphics tablet.
I have tried every combination of lead to port on the Card. The only way I can get an extended display is as above.