iPhone screen went blank

Iphone 4 screen is black, I was listening music and it just shut off. It still rings tho.my power button is stuck so i was using the dot thingy on the screen. My warranty is up so how much might it cost for me to fix it? and can anyone help me on how to make it work? it doesn't vibrate when it rings it just rings. I tried everything I know Please help. I can't hear no sound when it's ringing and it's not vibrating but i hear it when i use another phone to call it