Diagnosis
The local dimming or backlight system has failed or is stuck in an off state, a known hardware issue on some V-Series panels.
How to Fix It
Force a panel reset and check backlight settings.
1. With the TV on (sound playing), press and hold the 'Volume Down' and 'Input' buttons on the TV itself (not the remote) for 10 seconds.
2. The TV should cycle off and on. Check for picture.
3. If picture returns, immediately go to Menu > Picture > Backlight and ensure it's not set to 0. Set it to 50 as a test.
If That Didn't Work
This strongly indicates a failed backlight. Shine a bright flashlight at an angle on the screen in a dark room. If you can faintly see the image, the backlights are dead and the TV needs service.
Heads Up
Continually cycling power on a TV with suspected backlight failure can stress other components. If the flashlight test shows a faint image, stop and contact Vizio support.