5100 not charging while on

I've had my Inspiron 5100 for just over a year now, and I'm having a very strange problem. If my computer is on, my battery won't charge. When I turn the computer off, my battery charges, the charging indicator light blinks like it's supposed to, and everything is fine. When I turn it on though, the charging light turns off (unless it reached 100% before I turned it on, and then it remains on) and the battery stops charging. I've tried reseating the battery, but that hasn't helped. Is there an easy solution for this (I hope) or do I need to call Tech Support? Thanks!