Help battery problem

Hello to everyone! The battery of my ipod touch 5 was damaged. So I decided to change the battery by myself because the warranty was expired. My friend told me that he was able to change it. But after the change, ipod will not turn on.. Only if it is connect to power it turn on, but appears always the apple logo, and then it turn off.. endless.. it's a loop. what happens? My friend damaged the new battery? Help me please! (i'm sorry for my english but i'm italian.. hope i explained well the problem)