Let's work around the issue, the product is not faulty by default, obviously this issue is present in some system and not in others and we don't know exactly why.
In the FMC do you have message? like loading database permanently showed? and never really loading it?
The screen is just blank with no information?
If loading database is present and do not load, please go to folder C:\ProgramData\Lockheed Martin\Prepar3D v4 (please note that the ProgramData folder is a hidden folder, so you'll need to change the visibility to see it) inside this folder there should be a file called dll.xml, if you open this file using a text editor (like notepad) you'll se the code, please check if the lines:
If those lines are not present please copy form here and paste in the file just before </SimBase.Document> line. (if you don't know or sure on how to do this you may also send us the file and I'll repair it and send back to you.).
Once done please check if the FMC is working, If still don't work, please download the following file from the link and paste it in the simulator root folder, usually C:\Program Files\Lockheed Martin\Prepar3D v4
Please, if nothing of the previous procedures work, let us know to find another solution.