Ti 83 plus texas instrument calculator won't turn on?

at first it still turned on, but only sometimes. then sometimes while it was on it would just suddenly turn off even while i was still using it. now it won't turn on anymore. i assumed there was something wrong with the batteries so i changed all of them, except now it won't turn on. i tried all the other methods like pressing DEL or CLEAR or 2nd, but it still won't turn on. any suggestions?