i was deleting some apps and when turning off the phone (i heard it's best to do when adding/deleting apps) it no longer turns on. when i press and hold the on/off/sleep button it just displays the apple logo and nothing else, then disappears after a few seconds. the home button doesn't do anything. when i press and hold down both the home and on/off button it, again, just shows the apple logo... what's goin on?