To start with, I would suggest zapping the MA3 copy you have, then download and reinstall a new copy. (Make sure you have your Serial No.)
For years now, when confronted with strange graphic problems, I've often found that reinstalling the video card's graphic drivers, followed by reinstalling DirectX, then re-booting...
IN THAT ORDER, more often than not, can provide a solution.
Please have a read through this thread....
https://www.feldoncentral.com/forums...eta.zip&page=3
It worked for Mark on that occasion, and it has often worked for me. - It might be worth trying.
I have no problems running MA3 on my dual monitor setup.