The Add On Manager and Couati are there?
That's ends every discussion about installation, antivirus, settings, etc. If you have both menus, that means everything's running normally.
The only possible explanation for GSX not coming up are:
1) You haven't installed GSX. If you haven't, you would see the Couatl menu, but no "GSX Settings" and other GSX menus under it.
OR
2) There's a key conflict, either with some other product, or between GSX itself, if you redefined the GSX default key in the past, before GSX had two hotkeys. You can check this in the "Key assignment" menu under the Couatl menu. Be sure the two GSX hotkeys are set differently. By default, they are CTRL+F12 for YouControl and CTRL+Shift+F12 for GSX direct.