First, try changing your sound volume in the in-game settings. You can do this by clicking on the ESC-key on your keyboard > Options > Sounds and then turning up the bars. If that doesn’t help, you might want to check volume mixer settings on your computer. In order to do that, you will need to log in to Star Stable and then tab out, so that you can access the desktop.
On the task bar at the bottom of your screen there is a little speaker icon that you should right click on. Once you have done that, click on Open Volume Mixer. A small window will pop up and you should see Star Stable as an option as well. If the bar is at the bottom or the speaker icon has a tiny not allowed sign next to it, it means that you have no sound. Turn it up and you should be able to hear the in-game sounds again!