General Techniques for Troubleshooting Your iPhone
If your iPhone is behaving oddly or erratically, it’s possible that a specific component inside the phone is the cause. In that case, you don’t have much choice but to ship your iPhone back to Apple for repairs. Fortunately, however, most glitches are temporary and can often be fixed by using one or more of the following techniques:
Restart your iPhone. By far the most common solution to an iPhone problem is to shut it down and then restart it. By rebooting the iPhone, you reload the entire system, which is often enough to solve many problems. You restart your iPhone by pressing and holding the Sleep/Wake button for a few seconds until you see the Slide to Power Off screen (at which point you can release the button). Drag the Slide to Power Off slider to the right to start the shutdown. When the screen goes completely black, your iPhone is off. To restart, press and hold the Sleep/Wake button until you see the Apple logo and then release the button.
Reboot your iPhone hardware. When you restart your iPhone by pressing and holding Sleep/Wake for a while, what you’re really doing is rebooting the system software. If that still doesn’t solve the problem, you might need to reboot the iPhone hardware as well. To do that, press and hold ...