Your iPhone may occasionally lock up and become disabled, preventing you from using any of the device's built-in functions. Fortunately, it's possible to correct this problem with the two buttons built into the device.
Press and hold down the circle button, located below the touchscreen, and the small button at the top of the screen. Continue to hold these buttons down as the iPhone turns off.
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Wait a few moments, then press the circular button. After a few moments an Apple icon loads onto the screen. This performs a boot cycle that takes several moments.
Slide your finger across the "Unlock" option when the iPhone has finished booting. The main screen appears, allowing you to again use your once disabled cell phone.