Screen has black box with greek letters on channel

go to the Menu and you should find it.

swap out the box as it could be the problem and if it never does it with a DVD being played it is not likely to be the set.

turn closed caption off on tv & cable box

Turn off closed-captioning. You'll find it's set for "text" right now, probably from hitting a button on the remote without realizing it. The set is blanking the screen for the text which doesn't show up. (In your case sometimes it does. You're the first person who's ever seen anything that I've responded to!) On channels and programs where captioning isn't being sent the box doesn't show up, so you don't know you have the trouble.

Try and turn off the closed captioning. I had the same problem and it turned out that the closed captioning was on t1 instead of OFF. Hope this helps!!!!

You have the closed-captioning turned on and set to "text" mode. It's easy to do on Zeniths because many of their remotes have on button just to control the captioning. Go to the caption settings and turn it off or set it to "caption" mode if you want to use it. Then the box will be gone.

(What's happening is that in text mode, the screen is blanked out in the area where the text would go, but there isn't any text being sent by the station. On channels where no captioning at all is used, the box never shows up.)

it is the closed captions on the tv. it is set to closed caption text. turn it off

Check to see that you don't have any channel locks or parental parental permission measures deployed. If so remove them, this includes V-Chip, and Parental lock out on the remote, and check your TVs menu items. What channel are being affected by this problem? Give channel number and channel type.

Thank you,

Shuttle83

The aspect ratio (zoom) button on the cable remote had been changed. On Brighthouse the # button toggles through the zoom settings. It's not a tv issue, it's a cable fix.

Ve al menu de la tv y checa si esta activada la funcion TEXT si es asi desactivala suerte.