How can i fix my nintendo ds lite?

My Ds lite has been lying unused for months and when my daughter tried to use it, it wouldn't charge. I bought a new charger and when plugged in it looked as though it was charging as the light was orange but when it should have been fully charged with a green light showing the lights all went out and when tried to turn it on with a game in it, it would not do anything!! Do you think it could be the battery? And could it be replaced easily and cost minimum? Please help!!

Shelley Sutherland
January 2009