Diagnosis
This is usually a panel or signal source issue, not a total backlight failure since you can see it's on. The TV is receiving audio but the video signal isn't making it to the screen properly.
How to Fix It
First, power cycle everything. Unplug the TV from the wall for a full minute. While it's off, also unplug any devices (like your cable box or game console) from their power and from the TV's HDMI ports. Plug just the TV back in and turn it on using the physical power button. If you get a picture on the startup screen, then plug your devices back in one at a time to find the culprit.
If That Didn't Work
Try a factory reset. With the TV on (even with a black screen), press and hold the physical power button on the TV itself (not the remote) for about 5-10 seconds until you see the LED light blink or hear a click. This can sometimes force a reboot that clears a software glitch holding up the display.
Heads Up
If you only get a black screen with specific apps (like Netflix) but the home menu works fine, that's a different software bug. Try updating the TV software in the settings when you can get a picture.