I had the same issues as described in this thread (no gear appearing, most controls not working), although I am using Prepar3d (P3D) rather than FSX. My issue was to do with SimConnect, which seems to be an interface for 3rd party utilities to connect into FSX/P3D.

In my case, I had to manually install an older version of SimConnect for FSX, which for me was located at: C:\Program Files (x86)\Lockheed Martin\Prepar3D v3\redist\Interface\FSX-SP2-XPACK\retail\lib\SimConnect.msi. After doing this everything worked fine. I purchased P3D / the 737 package today, so everything was a fresh install.

Thought I would leave this here in case it helps anyone else in future. Bumping this particular thread because this is what Google was bringing me to.

Cheers.