Sometimes when the battery dies, it takes the entire thing with it. Had a case with a laptop once, a Dell, where the battery was pretty well dead and was making it so the laptop wouldn't start up at all, with or without the battery.
Of course if it's been unused for several years, that too can take a toll on things. If it's 3+ years old, and non-functional, it might just be time to break down and get a new laptop. Getting it fixed is likely to cost a good chunk of what a new one would cost.
I have a Panasonic Toughbook CF-50 next to me that was used through part of the Iraq War and it's been sitting for the past three years here at home and I was wondering what would cause it to not start up. Nothing happens when you hit the power button. I've tried resetting the power management unit but it didn't help at all. Im pretty sure the battery is done for however even with the power cord it still wont work. Nny ideas? Please help!