Have you checked that the TV isnt Muted/ Volume turned to 0 ? i would check in the menus if that is the case.
If this is not what is happening i suggest you surf over to the Goodmans website at www.goodmans.co.uk/
to see if there is any troubleshooting/FAQs on there. if not, i would call Goodmans customer Support, their number is located on the said website !
Hope This Helps !?