What happened to all of the voices? I only hear three!
You’re probably in Offline ATC mode.
No, I tried both modes. For a long period of flight, only one voice was working!
Offline ATC will work correctly only if your local Windows Installation is not corrupted - since it uses the built-in Windows Voice Pack based upon your OS Localization (i.e., US English, UK English, etc).
Sounds like you may have a 'Net connection issue or the sim is. I’d probably reboot the whole PC, verify connectivity, launch the sim and try again using Offline.