In P3D v4 the GSX sounds doesn't work..
So you problem is exactly the opposite of the one discussed in this thread, which complained of sound too loud.
I have set the two .waw files to off. no result
Well, of course no result. This would be the solution to get rid of a sound, not to fix missing sounds.
I have searched for no sounds in GSX forum and no results...
Of course, since it's not a GSX problem. You might simply have selected the wrong audio device in the GSX Sound settings, which is quite common if you have several audio device, and the default one is not properly set in Windows.
Be sure you have select the audio device you want to use in GSX, then exit and restart the sim.