Sounds like the LCD is broken. You need a new one
Parts
http://www.googleadservices.com/pagead/aclk?sa=L&ai=CVMKWusSZVrOGHYOo-gOoo62YCIX9y7UH_a2KnM8B5eSevZoDCAQQAiD4mYsSKApgybbgiZSkmBOgAaO1lfYDyAEHqgQnT9CyO56HtrDhsCmirU7Xl6UVyeU0a4laOmuRZrUvHStPol3KMdGNgAWX4LwLwAUFiAYBoAYm2AYCgAfFyuoJkAcDqAemvhvYBwHgEu2BhIjEzJDodQ&ohost=www.google.com&cid=CAASIuRoBl6VQdkphSgGfRxtT_cpnpvRJFQVhfgNUltZ7NrbKMI&sig=AOD64_0gMTwOE7qWMfg_ohcS2LVm0-TbkQ&ctype=5&clui=3&q=&ved=0ahUKEwikxtaQva3KAhVDxGMKHU4xDnIQwg8IHw&adurl=http://www.repairpartsplus.com/Replacement-LCD-Assembly-for-Galalxy-Mega-6-3-B-p/GPS12601.htm
Labor
http://m.youtube.com/watch?v=KqQwa2SZPhE