Screen of my IPhone went black and now it won't turn on, what is wrong?

The screen on my IPhone 4 went black and now it won't turn back on. It didn't get wet or anything Please Help!

Added (1). It was fully charged when this happened AND when I plug in it will not even light up.

Did you charge it?

Its dead…

Hold the power button and the home button for 11 seconds then it should turn on