I have a similar problem, but in my case I know what generated the problem. I just do not have any ideas on how to fix it. I also have a second TV off of a Dish 322 box. Now all that I am getting is a channel of snow.
The problem started on Friday when I had Earthlink (done by Time Warner) cable internet installed and they shared that run of coax to supply the internet to an adjoining room. All seemed very smooth, but later when the TV was put on, snow.
I had a Time Warner guy come back and check the installation, but he said there was nothing he could do. I called Dish Network and checked a few things, but there were no solutions. Of course they offered to send someone out for $95. Sadly, this is an old TV and only has 69 channels. I did note that when I reset the modulator to 68 and 69 I was getting a very poor Dish program. When I disconnect the internet from the splitter feeding the line the Dish signal comes back to the TV, though it is snowy. Not as clear as it used to be. I am guessing that has to do with the extra splitter that is in the line.
I can think of two simple solutions. First, get another TV that has more than 69 channels. The second idea would be to run a separate stretch of coax from the receiver to the TV. That might mean going attic and trying to fish cable to outlets, fighting squirrels and so on.
Any other ideas on what would be causing this and possible simple solutions? By the way, the internet works great.