I did not have the second monitor in FS set to the same resolution, even though it was set on the desktop.
I was not aware, that I had to set the secondary display, in the FS/settings/display/.hardware, to the same res as the primary. I could drag the panels across, but they were not active, after making the change, I can now, after many years, use them. I had asked a number of people for advice, but have, only now, got the answer.
Now I am back to before square one, as FSX is not using the secondary screen, i.e.:the screen is blank.I suspect my system hardware is not man enough to do so. So, for FSX, I am back to one screen, unless a triplehead2go is the answer, this uses one of the video cards output, whereas I am currently using both.