Sky boxes are pretty robust check the dish feeds are properly wired and all other connections are good then try this. With tV on and showing Sky do the following.
Unplug/switch off mains power to sky box, hold down the "back up" button on the top of box (do not let go until instructed). Reconnect mains power, keep finger on "back up" after a few seconds you will see a row of LEDs illuminate on the front of the box, on TV you will see white text on black background that says "do not disconect mains power sateelite system updating" or similar. then release the back up button and leave the room for 30 minutes. when you come back box should be in standby, turn the ox on with remote (can take a few minutes for it to sort its self out) then you should be away and working. IF not check dish feeds in services menu if both good you need a sky engineer out if both bad you need a sky engineer out if one good and one bad swap the 2 feeds (disconnect power to box before you do this) if the fault moves you need a sky engineer (and a new LNB), if the fault doesn't move you need a sky engineer (and a new box)
TomS, March 2013