phone not starting up after broken screen

[cypry1994]

hi their i have just got a 2nd hand galaxy s4 and put it on charge when i bought it without a sim in then put it straight in my pocket as i was going to go to pick a sim card up,as i got in the car i sat on it and now the screen has hairline cracks under the surface in the display.i put a sim in and the display stays black but the buttons at the bottom light up and vibrate when touched.is this a new screen job and how much am i looking at? thanks Josh