my macbook is not turning on!

I have a 2009 macbook. the last 12 months I wasn't at home so my mac was mostly off. after 6 months i was back home for a little while and turned it on and it worked. now after another six months it's not turning on when i push the start button, even when it's connected to a power source. when it's connected to a power source the LED is green.. which usually says that the battery is full. my sister told me that she turned it on one month ago and it worked. please help me i miss it very bed after one year wondering all over the world without it.
Thanks ahead.

The battery may have died during the time it hasn't been in use. I don't know that for sure but it does seem like that's what may have happened. Take it to your local Apple store and let them test the battery for you.