Sony Bravia won't display anything but, it's backlit and plays sounds.

It seems to be a remote possibility, especially after the reset, that your TV has gotten trapped in Picture Off mode. Check the power options menu and see if this is real.

How is the backlighting accomplished ? Through fluorescent lamps or through light emitting diodes switching ?

Well that's the thing, I can't even see the menus, volume bar or ANYTHING that gets displayed. I do see a backlight and hear sounds, though.

I tried unplugging it for 12 hours and still does it.

And the TV is an LED-based LCD. this is the model:kdl-40EX523

You do not have to see anything on the screen.You can follow the path to the Picture mode. Just check the User Manual of the TV set. Pick up the remote control unit and pretend browsing through the menus. Take a couple of seconds between button presses because it may take some time before the menu changes on the all-black screen.

Sometimes my computer's monitor goes blank due to whatever reason it may be. I know the path to restart option in Windows. So I start with the Windows button on the keyboard and using the arrow keys ( left-right-up-down ) I navigate to the restart option and press enter.

Anyway, as I told you, this was a remote possibility because resetting the TV should have returned everything to the factory mode. But wait. How did you do the resetting ? Isn't it a menu thing, either, which you can't see ? Is there a physical reset button on the TV case ?

Yeah, I`m sure the tv got reset. I had to hold up on the controller and then press the power button while keeping my finger on the up arow key. I think it might be broken for good.