There is a "virgin" copy, or the file that the sim installs in the proper location, of the Scenery.cfg file, located in the FS9 root folder. Do not change or alter it in any way. If you want to look in it, do not use any sort of word processor. Only ever use NotePad (included with Windows), or NotePad++, a freeware program.
You can take and COPY (not move, copy) the file to it's correct location manually. I strongly advise you to make a copy of the file that is already there, if you do. Or rename it. Something to save it, even if it's become corrupted somehow.
If you do this, bear in mind you will be back to the original installation of FS9 when it comes to scenery. None of the scenery you had added to your Scenery Library will be present any longer. You will have to add it back in manually. The default FS9 scenery will be there, just nothing you had added. Including payware, if any.
In Windows7 Home Pro, if it helps, the Scenery.cfg is located here: C:\Users\<YOUR_USER_NAME>\AppData\Roaming\Microsoft\FS9
Good luck!
Pat☺