Samsung galaxy note 4 locked and shutting down and on automatically

[AC Question]

my friend sent me galaxy note 4 at &t carrier. when I tried to unlock that phone at local dealer.it was not done but problem arise that phone is automatically switched off and on by itself. so anyone help me out of this problem

 

[B. Diddy]

Welcome to Android Central! Here's AT&T's unlock policy -- see if the process there works for you.

When the phone randomly reboots, is it getting you back to the homescreen, or does it get stuck on the Samsung logo, then reboot again? Have you already tried a new battery?