771 signal on one, but not all receivers whats up with that!

it's driving me crazy.  we had the power blink on and off about a month ago.  noticed the next day that diirectv was not working.  so reset box, unplugging cords, etc.  called support, checked all the connections, (three times) tried the test channels.  nothing worked so we scheduled a service call.  next day i went out and loosened then re tightened all cables, and ground wires- and it started working.  no local channels.  next day no tv again.  downstairs tv works, so i brought that receiver up and plugged it in- it works fine.  realized at that point that the ac cord unplugs from the box itself, so i assumed i had reset it- installed the original receiver, and it worked.  turned it on the next day- had a picture, yet full of blur- and then blank.  tv in basement still works fine.