If there is a masthead amp(booster) or active powered signal splitter in the roof space the previous people may have taken the power pack that powers it all with them when they left. It is a common problem finding the new owners have no or bad tv reception when they move in, the power pack usually plugs in say the loungeroom tv wallplate with the injector and feeds the low voltage power the amp via the coaxial cable. Depending on the splitter if there is one you may have to find which outlet passes the power to the amp ,
some pass power on all points others only the one wall point.
the previous people would have had good tv reception you would think.