It's not muted, is it?
Mute Audio: The Mute Audio control is now remembered for each keyboard shortcut. Audio can be muted or unmuted during a preview by clicking this button; when you do so the state of the Mute Audio control is applied to the shortcut that was used to start that preview, and will affect the next preview you start with that shortcut.
Nope, that was the first thing i checked. It does not seem to be muted. Still not sure what's wrong.
Check your audio hardware settings in the preferences.