ibook has been off for a while, now it won't boot up

almost 2 years ago i bought a new macbook. i let my little brother take my g4 ibook and use it because it was still in fairly good shape. he used it for a while but then turned it off for around a year and stored it in the closet. now i was trying to turn in on and it won't boot up all the way. it goes past the grey loading apple screen and then stops on a blank blue screen. does anyone have any idea what could be wrong with it?