How to Restart an iPhone 4
When your iPhone experiences a minor glitch such as a screen lockup or it doesn't seem to pick up a signal, you can often resolve these issues by restarting the device. Restarting the iPhone is a simple procedure that requires to no technical expertise. If restarting the device does not return the phone to full functionality, you may need to install the latest software updates or restore the iPhone to its factory settings.
Press the "Sleep/Wake" button on the top of the iPhone. A red slider-bar appears.
Tap and hold the button on the bar and slide it across the bar to turn the phone off. Wait for at least 30 seconds.
Turn the phone back on by pressing and holding the "Sleep/Wake" button until the Apple logo appears.
Repeat these steps if the first restart has no effect. If you continue to have issues, consult the user guide for your iPhone and make sure you have the latest software updates.