If your sound is not working, it could be that Fatdog64 just doesn't have a driver for it. Or more likely, the volume is muted or the wrong sound card has been chosen as the default. Even if you only have one sound card, often that card will have several functions driven by different drivers, so it looks like multiple sound cards to Fatdog64.
To adjust the volume, open AlsaMixer, found under Sound in the Control Panel or by right clicking on the sound icon in the tray and selecting "Alsa Mixer" Settings. This application does not use the mouse, you'll need to use the arrow keys to move and adjust the volumes. The m key mutes and unmutes a channel. Note that you can turn the volume up on a channel and still have it muted, so make sure that mute is off. At the bottom of each channel it should show 00, if it shows MM it's muted. The volume icon in the task bar only adjusts the Master volume, not any other channels.
To select the default sound card start the Fatdog Default Soundcard Wizard, found in Sound in the Control Panel. Select the device to use as the default and then use AlsaMixer again to make sure everything is turned up and unmuted. You also use the same wizard to send audio to a bluetooth device.