James, I saw this entry by Tim Capps on the 707 forum, I wonder if it may work for you:

"PROBLEM SOLVED. Sometimes when you uninstall something, FSX files get sucked into the void, too. This is often the cause for BLACK GAUGES or, in my case, BLACK CONTRAILS. In the A++++ library, search for "gauge recovery." Run the simple program that installs all your original GAUGES and EFFECTS that might have gone missing. It doesn't mess with anything else; just restores your FSX to what it should be. It fixed my problem in less than ten seconds."

Hope this fixes it,

Nathan.