Your P3D registry keys are probably missing/corrupted/pointing to the wrong folder. You can activate logging in the installer, this way:
- Open a command prompt ( start -> CMD -> enter )
- go to the folder where you have the installer, for example:
CD c:\Users\Yourname\Desktop
Assuming you put the installer on the Desktop
- launch the installer with this command:
gsx_fsx_setup.exe /log=install.log
This should hopefully create a file named install.log on your Desktop. If you have it, then send it to me ( via Email, please ).