What I found out too was when I reinstalled GSX with a trial version, I went to the default airport and surprising me nothing turned up. Hot key was not responding...
Fairly obvious that no key would respond, if the keymapping is blank. The issue is, it SHOULDN'T be blank, especially after a reinstall, because one of the things the installer does, is to restore the keymapping entries if they are missing.
A possible reason why the installer couldn't do that, could be related to problems with your user account, like wrong permissions setting, or the account corrupted.
Do you run FSX in "Compatibility" mode ? If yes, turn if off.