The more details the better. Start with telling us what's on the other end of the cable you've attached to the magic eye. Is it running to a Sky box or something else and are there any wall plates, splitters or anying else in between or is it a straight run of cable? I've usually found magic eye problems in my house are solved by carfeully refitting the plugs on my coax cable at each connection. Just a single stray strand of wire can throw a spanner into the works.