Cell phones provide wonderful convenience when they are operating normally. However, like any other electronic devices, cell phones may experience sudden software or hardware lock-ups. Such difficulties may interfere with screen display, signal levels, and even keypad data entry into the address book or other utility on your particular device. A simple power cycle under such circumstances will typically resolve the problem.
Locate your cellular phone's power button or switch. Although the power button may be located along either the top or one of the side edges of the device, many modern phones provide a keypad button on the front of the phone.
Press, and hold for a few seconds if necessary, the power button until the cellular phone is turned off completely. Wait for 15 to 30 seconds and then turn the phone back on and allow the device to come back online fully. This is called a "soft power cycle."
Test your cell phone to see if this power cycle resolved the issue. If the issue hasn't been resolved, then you may have to perform a "hard power cycle" which involves the complete removal of the cell phone battery while the phone is running. Simply remove the battery and wait 15 to 30 seconds once again before putting the battery back into the phone and then press the "ON" button to reboot the phone. Removal of a battery in this way forces most devices to perform a self-check when being restarted.