This occasionally happens to us and drives me nuts. Sometimes it appears to almost lock onto the wrong satellite. The fix is to hit the button again and get it to continue searching, but it sounds like you already tried this. Occasionally, nothing works and for no apparent reason. I've done the roof things that Tim did a few times, but didn't find anything obvious.
When we first took delivery of the coach it wouldn't find a satellite at all. The dealer changed the antenna, announcing it was "fixed" but, when I turned it on, it still wouldn't find the satellite. The tech spent 3 hours running through diagnostics and, when he finally called King Dome, and they told him to change the control cable that comes out of the dome, which he did. I don't see a cable going bad, but either a plug wasn't tight or a wire had become detached from a pin in a connector.
It might be worth a call to King Dome to see if they have any ideas.