help, no picture on magnavox big screen

Hi all, I don't know much about these but I'll try. I have an older magnavox big screen model rh8524 ak08. it has power and sound but it has no picture. now you got the cable that comes from the wall to the tv, and on the other side of that plate there is a shorter cable that goes from the wall cable to a silver metal box on one of the boards. If I mess (jiggle) that cable at the metal box the picture will come on untill you turn off the tv, then you have to do it agian. obviously, I don't know enough to fix it myself, but I would like to know what the box is called so when I get someone out to fix it, i will at least have an idea of what they are talking about! thanks, Mark