Follow these steps to add scenery:
Start FSX
Once at the aircraft selection menu, select "Settings" from the panel on the left
Next select "Scenery Library" from the "Other Settings" library
This puts you into the Scenery Library listing. From here you select "Add Area"
Now Browse to the Addon Scenery folder and double click to open it so you can see all the various addon sceneries. Assuming you've left each addon scenery in it's own folder, double click the folder you wish to add so that you now see the scenery and texture folders (sometimes it may just be a scenery folder alone).
Now select "OK" and check to be sure that the "Directory" box shows the correct directory and scenery folder and check that the "Scenery area Title" box has a name in it (if not type in whatever you want it to be called in the scenery library list).
Now right click inside the area where the texture and scenery folders are shown and it should put you back at the library listing with your new addon shown at the top of the list.
Click "OK" again and it should refresh the scenery library and your addon will be installed.
Make sure you're doing all of this and then let us know what it does. Be aware that this assumes that you haven't just dumped everything that came with your addon scenery into the main Addon Scenery, texture and scenery folders, but left them in their proper texture and scenery folders as they were when you unzipped the initial scenery.