Dead? Won't start up.

try removing the battery, plugging it into a wall and then see if it starts up. If it does then the capacity of your battery is dead. the battery lights do not indicate the capacity of the battery it indicates the amount of charge the maximum capacity of the battery. so you could have full lights on your battery and only have 200 mAh. then you just need to buy a new battery or take away all the perks of having a laptop and use it without a battery

If you decided to get a new one, you need to fully charge and then fully drain the battery every time to get the maximum life out of your battery. Leaving your ipod, laptop, iphone(or cell phone) or pretty much any electronic device plugged into a power source all the time is a terrible idea, it will kill your battery years before its lifespan.

resetting the PMU is a great idea too. when you do get it to turn on you need to open your system profiler and on the left hand side select "power" and it will tell you the health and capacity of your battery and see if your power cable is working as well.

I would reccomened that u try to buy a new battery of charger. When I had the same issue it was the charging port so i bought an external charger. Try That :)