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There has been some tuner failures I understand so im told , so you may have a hardware issue .
Make sure that you dont have your LNB cross nulled incorrectly .
Watch out for box lnb fighting ...as in , a dreambox that is getting a split feed of the skybox ...and if its not setup correctly , may be sending 22khz signals or voltage switching that could confuse the LNB whats to be done by its internal service scanning.
Just a thought ...prob a hardware fault tho I think ..esp if nothing else has been changed . If you have a feedhorn that has no cover on it , its probably a spider ...very common problem with open feeds . Also , water ingress on the connection outside - check it aswell . hope this gives you a few things to cross off the list . Cheers