Thanks for input Tom I will mess around with the anti alias settings and see what happens.I remember something about this from a few years back - something about anti-alias settings and full screen mode. I jst can't remember (or find) any details.
Now that I've had time to think more about it, I think this happened on nVidia cards where users had the card controlling the AA and not the Sim. If I remember correctly, it happend with the card AA setting at 8 or higher - I think...
3 minutes later...
I found this discussion on a GeForce board:
https://forums.geforce.com/default/topic/362240/preview-screen-blank-flight-sim-2004-problem/