With the TV on and audio heard, try shining a torch at an angle close to the screen and check for any images on the screen.
They will be very faint if they are there so trying in a darkened room may help to see them.
If there are images than there is a screen backlight problem with the TV.
If there are no images, disconnect the power to the TV and use an Ohmmeter to check if the fuse on the tcon board is OK.
The tcon board is the board that connects the mainboard to the screen. There is one cable that connects it to the mainboard and two cables that connect the board to the screen. This board is used for the video connection between the mainboard and the screen.
Here's an image to show where the fuse (and its rating) it is located on the tcon board.
(click on image to enlarge)