Restart phone in Safe Mode, press and hold the Power key to turn on your device. When the Samsung logo appears, hold the volume up key to bring up the lock screen display. Then select Safe Mode.
If it is working in Safe Mode, there still may be corrupted data caused by a third party app. This is where you can remove and reinstall apps to see it it fixes the problem.
Your data cache mogjt need to be cleared follow the first few steps but instead of selecting Safe Mode, an option should be to clear data cache.
Give that a whirl and see if it restarts.
Final option is factory reset. Following the same as before but instead of Safe mode or clear data cache, there should be an option to wipe phone factory reset. I recommend doing an android recovery prior to try and save anything important to you that isn't being backed up currently. (Ask and i can suggest a few).
Hope this