We experienced somehing similar a couple of years ago. We were getting the dreaded "771 loss of signal" message too even in clear weather and we have NO trees to obstruct. Long story short, what it turned out to be was our satellite dish (over the years) had been bumped or whatever and was out of alignment! We had a Direct serviceman out to check things out, he replaced our LNB (even though he didn't really think that was it) and re-tuned the dish. NO more "771" messages since!
It's hard to say what's going on in your situation but this is what ours turned out to be. Good luck!!
Dan
