If its an LED and the LED bulb went out you would still be able to see picture it would be just very faint. Its not like a projector where you can swap the bulb and be set.
Shine a flashlight directly against the screen and look very closely in a darkened room. Let us know if you can barely make out a shadowy image of the program you're trying to watch.
If you cannot see anything, the mainboard or power supply would have died.
If you can see an image, it would be the backlight that died.