Why is my screen black on my iPhone

I dropped my iPhone 3 days ago and cracked the back on it but i have been using my iPhone all day the past 3 days and everything was fine on it besides when i dropped it and cracked the back and all of the sudden about an hour ago my phone started running slow, i was going to turn it off then back on but my phone locked then it wouldn't light up or turn back on or anything i tried taking the back off and pushing everything down and i plugged it in to multiple outlets including my computer but it didn't do anything and i don't know what else i can do because i'm not sure why it would just go black like that. Any suggestions ?