How to Restart or Reset Your iPhone
Sometimes, you may need to restart your iPhone. And if that doesn't work, you can try resetting it. If your iPhone acts up on you — if it freezes, doesn't wake up from sleep, doesn't do something it used to do, or in any other way acts improperly — don't panic. You have some tricks you can try.
Apple recommends trying to restart your iPhone before you try resetting it.
Restarting your iPhone
Just like restarting a computer often fixes problems, restarting your iPhone sometimes works wonders:
Press and hold the sleep/wake button.
A red Slide to Power Off slider appears on the screen.
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.
Resetting your iPhone
If your iPhone refuses even to restart, you can reset it. Resetting your iPhone is like forcing your computer to restart after a crash.
To reset your iPhone:
Press and hold the Sleep/Wake button while pressing and holding the Home button on the front.
When you see the Apple logo, release both buttons.
Your data shouldn't be affected by a reset, so don't be shy about giving this technique a try. In many cases, your iPhone goes back to normal after you reset it this way.
Remember to press and hold both the sleep/wake button and the Home button. If you press both and then release them, you create a screen shot — a picture of whatever is on your screen at the time — rather than reset your iPhone. (This type of screen picture, by the way, is stored in the Photos app's Camera Roll.)