Go to the app you started last and complete the action. Shut off iPhone and turn back on if that doesn't work. Wait a few minuets and it should go away. I was trying to send a big email to my friend and the mail kept closing down so I restarted my phone. As I was restarting it, it wouldn't turn on so I touched the power button. DONT TOUCH THE POWER BUTTON. Press the home button and the power button at the exact same time and hold until the apple symbol shows up. The rings around the edge are it's turning on and off effect going berserk. Give it a few minuets and it should go away