Boot to recovery mode and wipe the partition cache. That will resolve most issues.
Restore your backup.
If you don't have a backup, you should take note and do so in the future. You could try "dirty flashing" just the system files or a custom ROM. That will mess up installed apps but is likely to make your device usable and leave user files and photos intact.
As a last resort, try writing a full, stock backup to your phone with Odin. You could also try getting your phone repaired if it is under warranty, however if you have rooted it or incremented the Knox counter some carriers or Samsung may refuse you warranty service.