Were you watching digital, sky or virgin when the message came on.
Are you sure you haven't accidentally selected the wrong source eg moved to HDMI 2?
Secondly what is the model of your TV?
Can you confirm if other TV's in the house are still able to get signal, just to rule out an antenna issue?
Ok, does your aerial go through an amp or is it a straight cable from the socket in the wall to the aerial on the roof?
I would look to re-tune your TV, and see if the TV is then able to rediscover the channels.
Whats the make and model of the TV Tom?