Dou you mean default FSX (planes, scenery) is running but you can not see any third party addon?
IF YES, it seems as if the autoinstallers of these addons are not directing to the right adress where the FSX program folder is.
In advance I give some information.
First, look for all files installed by FSX.
In a normal installation (C: drive with the Win7 OS), you have:
The program is in C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X
But also you have in Win7 four folders:
The files containig flights and other ítems : C:\Users\YOUR USER NAME\Documents\Flight Simulator X Files
The scenery files (you need actívate "view hidden files" to see it): C:\ProgramData\Microsoft\FSX . Here is scenery.cfg
The shaders files: C:\Users\YOUR USER NAME\AppData\Local\Microsoft\FSX
The file containing amongst others FSX.cfg : C:\Users\YOUR USER NAME\AppData\Roaming\Microsoft\FSX
You
must have this last four folders in the same partition with the OS, but it is posible to run the program in other HD or partition. (I have two FSX installations, one in C: and other in an external drive)
So check in C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes if the 3d party addons are really in this folders. Some autoinstallers don't allow to choose where to install the addon.
IF NOT, maybe is a registry problem and the addons have been installed out of the FSX program folder.
You can use either the Flight1 free registry repair tool:
http://www.flight1.com/view.asp?page=library or the more consistent free FSX registry utility from Tweak FS
http://www.softpedia.com/get/Tweak/Registry-Tweak/FSX-Registry-Utility.shtml Good luck