*Tried to use the HOT key to call up the GSX and You Control Menu - nothing happened.
This sentence leads me to believe that you have all your GSX and Couatl menus available, which clearly indicates GSX is working. The reason why you did all these stuff, and haven't solved anything, it's because if you are only missing the in-game menu, it's NOT a GSX problem or has anything to do with it!
This issue has been discussed so many times on the forum, and it's a known P3D installation bug. If you updated it using only the Client installer, no 3rd party application that use a menu will be able to show it, because LM haven't included the updated files required by the new Scaleform (transparent) menu in the Client installer.
In order to fix this, you must:
- Uninstall the P3D Client
- Download either the P3D Content file or the P3D Full installer.
- Install the Content, then reinstall the Client or, if you downloaded the Full installer, just the Full installer.
If you downgraded just the Client, you are probably in trouble, because while older Clients can be downloaded, the older Full installers or the older Content installers are not available anymore so, you might have a messy mix-up of the newer Content (which supports the NEW menus), with the older Client so, unless you have still kept an older FULL installer that matches your client, you cannot fix this, and you don't have any other options than to update the whole sim to the latest version.
Which, in fact, would be the best solution, I cannot think why anyone would want to use anything else than the latest Hotfix 3, precisely for stability reasons.