After a reset the unit initially looks only for one frequency, 11428 H where it will download the postcode database and freesat channel information.
If you do a manual tune in non freesat mode for FTA TV channels I think a lot will be found. If you then search for only the 11428 H transponder and there is no signal then the problem is with the LNB or less likely with water ingression in the cable or the units signalling.