A hard restart can be handy and should be used if an app refuses to start or if your phone has frozen up completely.

Hold the Home and On/Off buttons together for around ten seconds, ignoring the slide to power off message that appears. The screen then goes black and the Apple logo appears.

Let go of the buttons and wait for the iPhone to start up and everything should be back to normal.

Try restarting your iPhone if it is being unresponsive