Screen turns black after a few seconds of being turned on

I recognize this is an old question but still has value since this comes up many times with multiple other brands as well. Since you still have audio and the screen originally lights up, this is most certainly a failing backlight. Once the screen turns black, in a darkened room, shine a flashlight at an angle against the screen. If you can still make out shapes or silhouettes, you know it is the backlight array. To replace the backlight you will have to dismantle the panel and replace the backlight strips. Sounds complicated but it is not. We would need to see the back of the panel etc. which in this case will not be possible.