How to get my iPhone 4 to turn on

My iphone 4 will not turn on. It's stuck on the screen with the Apple logo that pops up when your phone is turning on (black bacground, white apple logo). I deleted and re-downloaded the Instagram app and it was taking FOREVER to load. So I turned off my phone. Now its not turning on and is stuck on that screen.

Try plugging it in to charge, holding down the power button, plug it into your computer, call apple for help, make sure there's nothing wrong with the phone on the outside.