It sounds like you have a Phase III dish and LNB, if so you will need a Slimline Dish and a SL3 or SL5 LNB to get the HD channels.
Most, if not all of the HD channels are on the 99 and 103 satellites now, which the Phase III dish cannot receive, as it only receives the 101,110, & 119 satellites.
They have different LNB's for the slimeline dish, some models get 3 satellites ( SL3: 99, 101, & 103 ) and other models get 5 satellites ( SL5: 99, 101, 103, 110 & 119 )