DaveO-MM: Before launching the game, right-click anywhere on the screen. Check your screen properties and see if a second monitor is listed. If so, uncheck 'Extend my Windows desktop onto this monitor'. Go back to monitor 1 and make sure that 'Use this device as the primary monitor' and 'Extend my Windows desktop onto this monitor' are checked. Click Ok and launch the game to see if the issue persists.
Gave it a shot -- no dice. The second monitor goes dark, as it should, but Sacred still runs about 1/3 off the now-only screen.