Why does my phone have a blacked out screen

@latifebuleshkaj this could be as simple as a bad screen or as complicated as an issue on your circuit board. I would opt for a new screen, if the phone still works except the screen. It should still give you a sign of life when you turn it on etc.

To replace the screen display use something like this video

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.