DIAGNOSIS: No, your TV isn't dead. A white light means it's on, and sound means it's processing a signal. You're likely dealing with a backlight failure, or more commonly, the local dimming system has crashed, leaving the LEDs off.
FIX: First, let's try a hard reset. 1) Unplug the TV from the wall outlet. 2) Press and hold the physical power button on the TV itself (not the remote) for a full 60 seconds. This drains all residual power and resets the mainboard. 3) While it's still unplugged, press the power button a few more times for good measure. 4) Plug the TV back in and turn it on with the remote. Listen for the startup chime and watch the screen closely in a dark room—you might see a very faint image if the backlights kick back on.
IF THAT DIDN'T WORK: Shine a bright flashlight at an angle directly onto the screen in a dark room. If you can see a very faint image/menu, then the panel and electronics are working, but the backlights have definitely failed. This is a hardware issue that requires a service call.
HEADS UP: If the hard reset works, you should immediately check for a firmware update (Settings > System > Software update) and install it. Sometimes a software bug can cause the backlight driver to freeze, and an update may contain a fix. If it happens again after an update, it's almost certainly a hardware problem.