What kind of LNB does the dish have, one coax connection (SWM) or four connections (legacy)? Legacy LNBs don't need power inserters but they do need BBCs for each tuner. SWM LNBs don't need a BBC, but they do need PIs.
Also, make sure the red connector on the PI goes to the LNB (maybe called ODU) and the white connector goes to the recevier (maybe called IRD).