5510 earpiece has no sound

[banana]

I bought a 5510 on holiday recently that was already unlocked. When I got home I can't hear anything from the earpiece when making or receiving calls so I have to use the earphones all the time. I did work very briefly one day but nothing since. Everything else on the phone is OK. I would be grateful if anyone has any ideas. As you can probably tell I don't have a clue about any of this.

Thanks