It's one of two things, the more likely of the two is that that battery is
totally shot, laptop battery's are usually only good for 1.5 years then loose there ability to retain a charge. It sounds like that one's just done.
Unfortunately that those
batteries cost more than there worth, 100 bucks or more. The second possibility is the power cord, is that the original power cord for that? Or was on that was bought
aftermarket, some aftermarket chargers will only power your laptop and not charge. Also remove the battery and check for
corrosion. You can build your own battery
for a laptop if got a few hours time, and are good with a soldering gun. You get the
lithium ion cells you need for about 40 bucks.Follow the below link for a step by step on how to build your own battery
http://www.metacafe.com/watch/479447/laptop_battery_hack_youll_save/