gemini joytab no sound


We've got a gemini joytab running android v4.0.3 and we've lost sound. Go into settings and got volumes up to max but at side of volume slide its got a speaker with line thru it not sure if this just signifies that end of scale is mute or whether it means sound is muted.

Anyway no sound from media played and if try changing default warning tone its not producing any sound when changing between tones.

Anyone have any ideas?