Press "M" to see if that fixes it.

M is the default mute key, there's no visual indicator your game is muted, and for whatever reason the game remembers whether you muted it or not (even though there isn't an option in the options menu to tick/untick muting). This is what was wrong with my game and I had to press every key to see if any worked.

Try reinstalling DirectX if your game is still muted, make sure that you haven't turned the sounds off in the options menu, and make sure that your computer sound is on (and you haven't turned off the game sound in the windows sound mixer). If none of that works, make a bug report and hope it gets fixed I guess ¯\_(ツ)_/¯