||There are a number of causes of this problem, the most common being an issue with your aerial. Please check that your aerial is connected both in the back of the television in the correct socket and that it is connected to the wall. Other causes of this problem could be that your aerial is not pointing at the transmitter and needs adjustment by a professional or it requires a booster, Contact your local aerial company for further advice.
It may also be that you have inadvertently skipped the initial setup. Please consult your manual for advice on how to restart the tuning process for your particular model. If you do not have access to your manual you may find it here.