If the above method does not work, the LNB may have a fault.
Press the [SERVICES] button and then press    then [SELECT]
On Sky HD, press the [SERVICES] button and then press    then [SELECT]
Press the buttons in the sequence above exactly - do not atttempt to use [UP] or [DOWN]. Note that when you press the second 0 and 1 nothing happens on the screen until you press the final [SELECT]. This is a "hidden menu".
Phil S: Have you tried disconnecting the box from the mains for 20 seconds or so before reconnecting it again and allowing it to go through the usual searching for listings procedure? should though this not resolve the problem then it could be caused by water have gained access into the dishes LNB "F" connector and partially shorting out the band switching commands sent by the box to the LNB, this type of thing seriously restricting what you can view, as of course will also be the case if the dish has moved slightly out of alignment through having been blown by the wind, it only taking the merest fraction of movement to do this, the best way of knowing if this is applicable or not being to have a look at the signal check screen, both levels (strength / quality) being a minimum of 60% and with the quality never being under the strength, this indicating that the dish is slightly out of alignment.
However, more detailed advice can be supplied with knowledge of the type of Sky box being referred to, e.g: Standard, Sky+, or Sky+HD.