Is the speaker icon on the menu bar greyed out? If you option+click the speaker icon on the menu bar what options do you have under 'Output device'? Which one is selected? Look into the headphone socket, can you see a red light?
Speaker icon - volume control moves. Preference = Sound is not Mute. Another information: I maged to connect a USB speaker device, select the device in the Preferences ➜ Sound ➜ Output and Control the volume from the icon. But still no sound from internal Speakers and Headphone.