Searching for satellite signal ...(771)

I have a DirectTV D12 receiver, which has been unplugged for over a month, and now that I have plugged it in I am only getting "Searching for satellite signal...(771)" message bouncing around the screen.  No channel lineup or anything.  I have reset the receiver many times, checked all my wiring connections, and reauthorized the receiver.  Nothing corrected the problem.  This receiver travels with me in my RV and we have not had this problem in the past.  Please advise ASAP!