My screen is all black

As long as your top led light and bottom menu and back lights come on when plugged in but the display remains black...guaranteed your lcd has been damaged and needs replacing. Your lcd lies under the screen and is very fragile on Samsung phones. Very common for the glass to be intact and the lcd underneath to be damaged. If you hold it under a light you should be able to see some small crack/cracks under the glass.

LCD is likely to be broken, as from the sounds of it phone is still functioning, sometimes you cannot see the crack as it is around the edge or across the flex contact. The LCD on this model is quite thin and susceptible to breaking from drop damage unlike other iterations of the S model Phone's.

New Screen Assembly is needed I'm afraid.