Not turning on

i have a hp note book nc 6400 th batrey died on it while i was using it and whn i tried turning it on nxt time it did not come on i tried talking the battrey out and puting it on and then i put the laptop on charge there is a batrey lite of green colour which is on and is even on whn i take the note book of charge ,its basically not coming on the power button whn i try pressing it on its not coming on .......plzzzzzzzzzzzzz help its really important