First, be sure if you are installing using the latest Full installer (which we released just a few days ago), not from a previous installer you might have downloaded in the past.
Also, you said you are missing the Couatl/GSX menus. Do you have at least the Addon Manager menu ?
If you are missing just Couatl, the most likely issue is the antivirus, so disable the antivirus while installing, and configure it to exclude the whole Flight sim folder from scanning, before starting the sim.