GSX surely works without any problems with the PMDG 777, since it's an internally supported airplane. Since it's impossible to help you with such a generic description ("doesn't work" or "I'm having trouble" doesn't say much about your problem), the only possible cause that I can think of is:
- You are not using the current GSX version and/or never updated it using the Live Update feature. Just re-downlooad the full installer now, so it's sure you'll have the most current version
- You are using a configuration file you made, which is not needed because the airplane is supported internally, and that file might be wrong. Use the "Reset" function of the airplane configuration editor in GSX, to restore the default configuration that comes with GSX.
