Diagnosis
The backlight is working but the LCD panel is not receiving a proper signal. The main board or T-Con board is likely faulty.
How to Fix It
Unplug the TV. Remove the back cover. Locate the T-Con board. It's a smaller board connected to the LCD panel ribbons. Carefully reseat both ribbon cable connectors. Reassemble and test.
If That Didn't Work
The main board is defective. You need a replacement main board (part number EAX67177504 for this model).
Heads Up
The T-Con board is fragile. Do not touch the gold connectors. Discharge static from your hands first.