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.Slide the red slider to turn off the iPhone, and then wait a few seconds.Press and hold the sleep/wake button again until the Apple logo appears on the screen.If your phone is still frozen, misbehaves, or doesn’t start, do a force-quit:.First-generation iPhone or iPhone 3G: Force-quit by pressing and holding the Home button for 6 to 10 seconds.iPhone 3GS or 4: Press and hold the sleep/wake button until the red Slide to Power Off button appears, and then release the sleep/wake button. Don’t drag the red slider. Instead, with the red slider still on the screen, press and hold the Home button for 6 to 15 seconds.
At the bottom of the phone, just under the bottom edge of the screen, there is a Home button. On the top side of your iPhone, there is the Unlock button. Press and hold both the buttons simultaneously for a while. After a while you will notice that the iPhone has begun to shut down and restart.