Are you using custom rom?
Give a try. Just flash stock rom.
Go to download mode, and keep tapping on power button when you're in download mode. Tapping power button is to prevent your phone to reboot. Then flash stock rom via odin
One day, my sister got this problem too. So I concluded that the problem was in the custom rom. So, I flashed my sister's phone back to stock rom and everything went normal.
Sorry for bad English