Last three days a black box appears on the screen—upper left side... I have had to unplug the cable box to make the box disappear...
1st time it appeared in the early morning and 2nd time at 9pm
both times the TV and cable box were turned off, I came in turned each one on as I always do, and the black box was there.
I DO NOT HAVE CLOSED CAPTION TURNED ON!
Does your TV have a pip feature?
if so, maybe it got turned on?
Double check it.
Maybe someone hit a button by mistake.
Otherwise, if you have more than one STB, try swapping them around to see if problem follows box or stays with TV.