After battery change iPod dont shut off.

Hello !

I just change the battery of an ipod nano 4th gen and i was thinking everything was good but....

First when i plugged back everything i get 2 beeps and a white screen but the ipod still play music (as long as you know where to go). But after playing with it a little bit i leave it there and after a bit of time i've notice that the ipod was still on and theres no way to shut it off (untill the battery is dead empty).

What could be the bug ?????

Thanks to help.