LG TV turns on for a few seconds then disapears

Hi,

What is the model number of the TV?

If it is a LED TV turn on the TV and then use a torch and shine it at an angle close to the screen to see if you can detect any images at all when the screen is black and there is audio. The images will be very faint if they are there so trying this in a darkened room may help to see it.

If there are images then you have a backlight problem. This could be the power board (or maybe an inverter board) the LED strips themselves or maybe a problem with the mainboard telling the power board to turn the backlights off.