bought this tv recently plugged it in, plugged the hdmi cable to the virgin box and then to the tv, switched it all on, works fine including the hd channels. when i knock the box and tv to standby for any length of time it seems to reset because when i knock them both back on the tv shows the snowy screen with "no or weak signal" to get a picture back on ive got to press the source button and scroll through tv ext pc and select hdmi is this normal or should a picture come straight on as soon as i power up...thanx