I got black marks on the display

@shadowboy based on the little amount of information that you are providing, this sounds like a bad screen. Of course, we will need to verify this by seeing the display and checking on those black marks. Adding images to an existing question - iFixit Repair Guide

If it is the display that needs to be replaced and since iFixit does not yet have a guide for that, use something like this video Replacement screens are readily available at many online stores.

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 a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!