Vizio 42" tv has no picture but sound. What is

Did you check out the power supply for proper operation since both the audio and video are gone? If PS is good then the problem may very well be on main board.

Your Tv possibly have faulty y sustain board, just replace that board to fix the problem

Its the inverter board which is preventing the backlights from coming on very common issue. You can get the replacement inverter from www.tvrepairworld.com

common problem with no common or single answer===time for a repair shop or a tech.

I w having this same issue when watching a Blu-Ray disc. I found it to be dependent upon what picture mode the TV was set to. By this I mean certain picture modes would cause the TV to dim during dark scenes of a movie. Changing the picture mode helped a lot.

Y-Sustain or Z-sustain PCB.

is the cable in all of the way? sounds like something is interrupting the transmission. i know the tv is large but try using it somewhere else. this will distinguish weather the problem is the tv or the cable

did you ever get it resolve? I am having the same problem. my tv is a year and and 1 week old. I am so upset.

your TV was overheat. check secondary power supply inside chasis. check all the components specially thus budged capacitos.

It sounds to me that the unit has a faulty inverter board which could be due to an overheated/bulged capacitor. I would send in a claim on it to the factory if it is still under warranty.