Plugged in, Not charging?

so i have a dell inspiron laptop, and have had it for over a year now. i have windows vista, and whenever i plug in my laptop it says plugged in, not charging. i can't leave my laptop of the charger, or else it will not work because my battery level is at 3%. if any one knows anything that can help me, i'd appreciate it! and does anyone know how much a new battery would be, if that would be my case?