Try another monitor on your computer or video source.
Determine if the "black square" problem follows the TV or stays with the computer/video source.
I suspect that the Vizio TV may have a loose "connection" inside. Some component or trace/wire that works most of the time and then due to vibration, heat, etc. disconnects and the image is momentarily lost.
Thanks! It is a Vizio TV and no computer or other source involved, but will change out the cable box first. We will see if we can find a loose wire or connection in the tv if cable box switch does not work.