I start P3Dv2.5, go to a flight I wanted to do the whole day, place my aircraft at the gate, shut it down and set the parking brakes. Then I press ctrl+F12 to open up GSX, but nothing happens. Checked the "Add-ons" tab in the menu bar, Couatl powered products > GSX - Settings and GSX- Customize Aircraft, as well as Key Mappings are there. All FSDT sceneries I have work fine. It's just the window that doesn't want to appear.
If you have the GSX menus, it's means everything IS working.
Install new standalone Addon Manager (tried - no success), un- and re-installed GSX (tried - no success), again re-installed Addon Manager and reboot (tried - no success), clear all my VC++ 2005 packages and reinstall exactly as you say. Nothing helped. All SimConnects work fine. Please tell me you have an idea where the problem could be or that there is another way of opening GSX.
NONE of these would be needed because, the only reason to undertake such steps would be if the programs would not *start*. "Not starting", means you won't see their menus. Since you have the GSX menus, it means that GSX is running correctly, so none of these was ever needed.
The only possible reason why you don't see the GSX menu when you press the hotkey, is that you have ANOTHER addon in conflict which is using the same hotkey so, you must either change it in GSX, using the "Key Mapping" menu, or change it in the other addon.
Be careful not to cause an internal key-conflict by yourself, for example by assigning both GSX keys to the same key combination.
Another possible source of confusion, is that you cannot call GSX on a parking for a reason, for example the airplane being too big for it. Usually, GSX would warn you with an error message and a sound. But if you put the "Message Verbosity" slider in the GSX Settings all the way to the left, because you didn't like the messages, you wouldn't see such warning.