Laptop Powering up issues, please help!

Here's the scoop, I just bought a gateway 400sd4 laptop on ebay. It arrives, works good for 1 day. The laptop is supposed to be in great shape, except the battery is spent. So I shut the Laptop off, and take the battery out to look at the info. I try to plug in my laptop without the battery and try to start it. It doesnt turn on. (??) I then put the spent batter back in, and it doesnt turn on! It will not power on now at all.

This is so confusing because with it plugged into the wall, I get a colored light, which shows I have power, but the laptop doesnt turn on!

I dont know enough about the laptop because I just got it, I ordered a new battery, and hope that is the only problem (when the powerpack is plugged in a long time, the amber colored light then turns red, which means the battery is dead I guess.) Does anyone have any clue as to what this could be?? I hit the restart pin under the laptop, and I know it is not the motherboard connection. Please help! I hate Ebay!