5 days of pixelated picture

Suddenly 5 days ago the main TV has been pixelated, large tiles, sound cutting out. Happens on live and DVR tv.  We made no changes, didn't move anything, wifi working fine. Ensured all cords are tight. Have reset the modem and the tv box numerous times. Tried to use the Xfibity Assistant,  that is very limited and if you try to ask a question or answer not in a stock response, it starts all over.

Our TV box is the type with a clock in it.  Incredibly frustrating.