You don't say which airplane you are using: if it's internally supported by GSX, or you made a configuration file for it. Vehicles might not appear if the airplane is not configured correctly, which is something you must do (using the airplane configuration editor), before you can use an airplane that is not already internally supported by GSX. The airplane configuration editor will tell you from which source it's taking the information from.
If you are sure the airplane is configured correctly, check you have all the latest vehicles installed. If you are not sure, you can either download and install one of the vehicle update installers on the GSX page, or the full GSX installer.
If you are sure all the latest vehicles are installed, it's possible the problem is caused by an issue of video drivers and/or wrong settings in the FSX.CFG. In this case, try all the following:
- Update your video driver
- Reset your video driver settings to default
- Reset the FSX settings to default, by removing the following file:
%APPDATA%\Microsoft\FSX\FSX.CFG
This will force FSX to rebuild a new config with all default settings. After doing this, be sure you apply the HIGHMEMFIX tweak in the Addon Manager, save the settings and restart FSX.
If this still doesn't fix it, be sure you don't run FSX into any of the "Compatibility" modes. Every checkmark in the Compatibility tab of the Properties for FSX.EXE should be off.
