Used Slim Power Problems

Ok, so i bought this used slim (i know im being cheap but it was a really good price and he said it was all ok and i still will probably get a refund.) and i think the battery is dead. So i plug it into the wall and head out to dinner. I come back and turn it on first thing still attached to the power cord. It turns on and is so pretty. So i unplug it and it turns off . Hmm thats wierd. So i try and turn it on with only the battery as power, and no green light (no light at all). Very strange, so i try one of my batteries from my Phat psp and it wont work either, and i know they are fully charged (so i dont see how it could be the slim battery). Any ideas as to a possible remedy or quickfix without returning it since i dont want to fork over the money for a new one? Thanks for the help!

When you left it charging...did the orange LED light turn on?

hmm i want to say yes, but im not sure as i opened the packaging and plugged it in a ran off. The charging lite wont turn on atm so i am assuming not.

Edit: Forgot, i also have one of those wall chargers since i have 2 phat batteries, and the light stays green on it when i put the slim battery in it. So, either its fully charged (yea right) or something is very very wrong! arrg!

hmm, i took out the battery to show my roomate, and when i stuck it back in to show him, it powered on. Very strange. Hope it wont happen again, otherwise i might just cry! lol

ace: No need to double post so quickly.