@prudence since it does give you an error message, you know it is not a settings issue. This sounds like a failed fingerprint reader. You can use something like [https://www.youtube.com/watch?v=P1vC4YbNxBo|this video] as your guide.
Now, if that does not repair your fingerprint reader, you will have to do a deeper check. Here is the Samsung flowchart for the Fingerprint Sensor not working
[image|3024607]
Use the search function of your PDF reader to locate the components to be checked, from this document [document|30516]
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.
***Repair is War on Entropy!***