I too have a similar problems with last 3 to 4 tps since 2 weeks.
I have multi line connection. the primary setup box works fine, but the 2nd setup box has issue's.
It only affects the hd channels. I get the no signal error whenever I start the box and than after few seconds it starts working.It also happens while switching between HD channels
Update : Problem is fixed.
Thanks to dish tv customer care who responded expeditiously, called customer care at 3:30pm today and they were here by 5pm.
Apparently, There was a problem with the wire and I heard some technical jargon about the transponder being defective (I might be wrong, didn't listen properly).