Panasonic LCD TV . (Painswick GL6)

Am looking to take a Panasonic Viera 31.5 " screen to the tip this coming Friday . Unfortunately the TV has a habit of displaying "No Signal" even though we know there is a signal.We have.been unable to find out how to resolve. Perhaps someone may be able to fix. Comes with Manual and leads. Was used with a set top box which we no longer need. Live in Painswick.