Why won't my Samsung Galaxy tab 2 7.0 not charge?

My Samsung Galaxy tab 2 7.0 will not charge when it's on, when u turn it off it will charge just fine. Nothing happened to it, no water damage, or shock. I've tried everything I know to do and it will not charge while is on. It just has a red X over the battery symbol and when u check the status it tells u it's not charging. Please! Someone give me an answer besides going and buying a new. I need this thing.