When you install a new scenery, GSX will recreate the airport cache and, while it's doing that, you cannot use it. If you haven't configured the antivirus to exclude the simulator folder, and you have lots of sceneries, this can take a while, so you might assume GSX is not available, especially if you disabled the top text bar ( the Info text in the sim settings ).
So, first try to add the entire simulator folder to the antivirus exclusion list, which will make startup and the airport cache regeneration faster. If you have sceneries installed in other folders, you should add those folders to the antivirus exclusion as well.