Was the phone working normally beforehand? Was the phone dropped.
Could be the result of a failed update of some sort.
Do you have the User Guide/Manual?
Check the troubleshooting section.
I also did some googling and found the following link:
https://thedroidguy.com/2018/06/fix-samsung-galaxy-j3-black-screen-death-unresponsive-troubleshooting-guide-1072834
Google "samsung j3 black screen of death fix" for even more links.
I do not have a Samsung phone so cannot vouch that any given solution will work. Read carefully and be careful about what you try.
Otherwise contact Samsung for assistance.