A word of caution: The factory reset most likely changed the input setting so double check that you actually have lost sound. I would suspect a power supply problem initially as these are the most common. Also, are you sure that the back light is working? Use the flashlight method to see if there is an image on the screen. Again, I would suspect that the back light is not working. Once this is verified, we can then examine further and provide additional items to check.
Dan