Why is my screen black!?

The other day I put my phone in my teachers phone holder, and after class I grabbed it and went to the car. I looked at my phone and the screen was purple on one side. I went home and talked to my dad and he told me to let it sit, so I did. the next few day I kept checking it but it kept on getting worse and worse. I tried charging it but that didn't work either. now my phone screen is black, but I can hit the power button and still hear the volume being turned up and I can hear it when I click the home button. What should it do?