inspiron 1520 - to replace the battery or the ac adapter?

I've had my laptop for a little less than two years.  Starting a couple of months ago my laptop would not work unless the ac adapter was plugged into both an outlet and my laptop.  If the adapter was to get unplugged from either the outlet or the laptop, the system would shut down immediately.  When the ac adapter was plugged in, laptop would flash amber. 

Last week, my laptop suddenly shut off completely.  I went over to check if the adapter had come loose and it hadn't, and I could not get my laptop to turn back on.  When my adapter is plugged in now, every once in a while the green light on the brick will come on, but then it will die when I try plugging it into the laptop.  I'll unplug it from the outlet, and plug it back in again and the green light won't come on at all.  If I give the adapter some time, and plug it in the green light comes back on but will eventually fade again. I've checked the adapter for bent wires or frays in the casing, and there is nothing seemingly wrong with it.

My question here is do I need a new battery or a new adapter?  I'm not sure which to order and I don't want to waste my money getting a new battery when all I need is an adapter and vice versa.  Any help at all will be greatly appreciated.  Thanks