Why won't my nook charge?

So I plug my nook up and it starts to charge. The light comes on and goes to green to orange. But then it goes off and doesn't charge! My dad thought it was the battery. So he changed it out and he got it fully charged! Then I haven't messed with it for a bit. And then I go to charge it so my Daughter can play on it and it's doing it all over again. Sometimes when I replug it in it turns on and stays on for a minute while on charger but then says the battery is too low and is about to shut off! Please help!