Sometimes you may need to perform a soft reset on your iPhone 4 because your phone may be frozen and not unresponsive.
If your iPhone 4 is frozen and won’t respond, you may want to try a Soft Reset.
1. On your iPhone press and hold the Sleep/Wake button until you see the red slider appears.
2. Drag the slider.
3. Then press and hold the Sleep/Wake button again until the Apple logo appears.
Your iPhone 4 now have been soft reset. You can also try to perform hard reset it is still frozen.