I'm not sure about the internal LED's but what I would do first in this situation is:
Determine if the back-light is failing.
Have several devices hooked up to the tv and switched on.
Turn the tv on and listen for audio.
If no audio is heard then slowly cycle through the inputs pausing for a moment in between.
If you hear audio, use a bright flashlight near the screen and check for video.
If you see video, you have a back-light problem and will have to troubleshoot from there.
Checking for video with no back-light can be done without any devices connected by simply using the tv's menu for a video source.
Try this and let us know what you find. You may have a totally different problem but based on what you posted, this is where I would start.