I was playing around with my tv trying to set the color when I got the same black box. I think that it has something to do with the closed captioned text. Make sure it is turned off. Hope this helps.

You may have inadvertently turned on the "Closed Caption Text" mode. This inadvertently happened to me after I first hooked the TV up and was exploring its features - very frustrating as it is just aplain black box and the scant directions of the owners manual were unclear about this feature. I was looking for complaints of the picture being too dark with porr color quality, but found this black box complaint more than once. So don't feel too bad. Cycle the C.C. button on your remote until you see "Closed Caption Off" on your screen. The plain black box should then go away.