VIZIO M3D470KD TV TURNS ON, HAVE BACK LIGHT, V LOGO APPEARS ON SCREEN THE FADES AWAY.

Bad LED strip lights, bad capacitors or bad diodes.

SOUNDS LIKE A FAULTY CAPACITOR IN YOUR POWER SUPPLY

Bad capacitor probably

Do you have voltage (3.5V) on the PSON terminal when you push the start button on the TV...if you don't its the main board that has failed

Start with the power supply board first. That usually fixes the problem. No need tor the T-con board.

backlight inverter

My Vizio E322AR White Vizio Light comes on when plugged in, then slowly fades to "Off". I unplugged and replugged - same. I held down the power botton on the side, and plugged in... same. Vizio light comes on (White) and over 5 seconds or so... fades out to nothing.
Remote doesn't do anything, buttons on the side don't do anything.
Going to pull the back off and look for bad Capacitors, and test fuzes for continuity. Wish me luck ... will report back later with results.

Usually when a TV fails to turn on properly a lamp will flash a number of times which with the correct info guides you in the direction of the fault.

how long did you leave it unpluged

Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.