Why is my screen black after dropping and cracking it?

I cracked my iPhone 4 screen a month ago. It's worked fine, with the crack stemming from the earpiece area outward due to my money clip applying pressure to it in my pocket. I've dropped it a few times since then, and now the screen is black although I can still place calls using voice control and even use the touch screen using my memory of where things should be. Sometimes the screen will come on for a few minutes. A hard reset worked and then it went black again. I have also tried restoring it to factory settings. How do I fix this?