For the last week the tv will suddenly turn off and then restart. Sometimes it will start up again immediately, other times it gets stuck on the welcome page and other times it is a black screen with an arrow symbol. It is now doing this after 5 mins or less of tv watching. I phoned the helpline who suggested we turn it off at the wall, wait 20 mins and restart - this does not seem to have helped. Do I need a new box or is there something else I should do?