Toshiba Satellite blank screen can't get to the shut down

Hello,
my grandsons laptop just has a blank screen and the curser arrow on it when you go to nock it off it is still on the light on frount is just flassing when you press the on off button because you carnt get to the shut down have held the butten in and got it to go off now but dont want to put it back on its a Toshiba Satellite C850-1G2