We have the same problem. I phoned Sky and spent 30 minutes doing all the usual- switching off, re-booting, checking the cables and checking the settings. The diagnosis came up on screen that we aren't getting a full signal from the sky dish - she said it was probably that either the LNB or the connection cables from the dish are faulty. So.... we have an engineer coming to check it ... Monday week! (Although my location shows Turkey we are actually in UK at present)