Sky box saying that its not receiving any signal?

Hi all, I'm a long-time lurker on here for advice, but I've signed up because I have an annoying problem and maybe somebody has some advice?

I came home today to find that one of my sky boxes is not working at all. The blue screen is saying that there is no satellite signal being received, and '29' is being displayed on the top right hand side. I have two other boxes, a sky+ and another standard sky box, both of which are working fine. Before I went away on Thursday I noticed that the box was being a bit sluggish, and today it just wouldn't work at all.

The same problem happened with this connection before- the box started acting up before completely shutting down. The Sky technician came out and apparently put in a new box, and all was fine for about six months until now. I rang up Sky to be told that my warranty had just ran out and that it would cost €100 for a service!

I don't think the problem is the individual box because I have an old Sky box in the house from previously which I connected up and this also says that there is no signal. I checked the wires into the dish and they all seem to be fine.

If anyone could help I'd be grateful, cheers.