The GSX menu disappearing immediately is USUALLY created by having a "real" copy of the GSX packages in the Commmunity folder instead of a Symbolic link, which is how GSX defaults to when installed with the installer.
This second copy might be created intentionally ( by manually copying it, which is a mistake ) but also unintentionally, and the easiest way to create one unintentionally is to make a backup of the whole Community folder and later a restore, without being aware of how the restore method is handling Symbolic links. The default Windows copy/past folders, for example, WILL create a duplicate real folder when restoring.
GSX should never be disabled like this. Instead, if you want to momentarily disable it, Unlink it from the FSDT Installer, then Relink it. Unlink means selecting "Uninstall" and reply YES to the 1st question ( Unlink ) but NO to the 2nd one ( Uninstall ). This way, you can quickly enable it back without reinstalling it.
If you unintentionally created real folders for the GSX packages in the Community folder, which are folders without a small arrow on then, remove ALL OF THEM (all the ones belonging to GSX), enter the FSDT Installer and click RELINK. This will recreate the links are they are supposed to, fixing the problem.