Guide Shows HD Channels -- TV doesn't get them

   I purchased an inexpensive TV from Walmart---LED-LCD- TV ( LE24Ho60) for my daughters bedroom.  I borrowed the Directv HD receiver from another room and connected all with an HDMI cable.  When I get the guide for the channels ( directv remote) I see all the channels including, of course, the HD channels.  I set the TV to HDMI and get only the stanard channels.  If I try an HD channel, I get a "searching for Sat" ( or something  like that and get a 771 error.

  Connections are firm and I can't understand why I can't get the HD channels.  Something I have, or am doing wrong, I suppose but I can't figure it out.  Red the manuals---everything.  Anybody have a clue?  I would really appriciate it, even if it makes me look like a dumb@@@.

Thanks,     wiseman