Iphone 4s screen is black and wont work!

Hi, I'd plugged my iPhone 4s into the charger, and it was working just fine, I saw the red bar and everything. But then the screen went completely black upon having turned on. I can still use siri and my phone still works but I just can't see anything. I've tried the home and lock button to restart, and I do see the apple logo come up but when the restart has finished it just goes black to being a blank black screen. Any suggestions?

Also when my phone does work, the sound doesn't work. It appears and disappears on occasion, but mostly I have no sound unless I use headphones. Which I don't like to use for long periods of time.