Digital LCD TV & Digital TV Recorder Problems?

Hello we have just bought the TV & recorder we have connected the scart lead & Ariel to the proper sockets and it works fine the picture is perfect .The problem is after a few hours it just goes of & no signal comes on the screen .The problem seem to be when you switch from the digital box to the TV The TV Ariel is an old one could this have anything to do with it as i said the picture is perfect i have it on now can you help