Why Won't My iPhone Screen Go on?

I just dropped my iPhone 4 in a protective case, and even though it was in the case, after i picked it back up, the screen was black and wouldnt turn back on, i hear the connecting sound when i plug it in to charge it, but the screen will not turn on for some reason.
I've restored it and held home and sleep button for 10 seconds and that hasn't fixed it

Cases for iPhones are normally just to make it look pretty. When I dropped my iPod touch in its case, the same thing happened.

Iphone cases are generally used to protect iphone and you are searching for iphone 5 cases then you may watch out here. Many of us likes to use iphone cases for their safety reason.