A soft reset (turning the device off then back on) is similar to restarting a desktop computer and is one of the first steps in troubleshooting a device. In most cases, a soft reset won't affect data on the device, unless the battery is very low.
If the device won't power on or off, press and hold the Power and Volume Up buttons until the device powers on/off (can take up to 2 minutes).
Press and hold the Power button (on the left edge) until the 'options' menu appears then release.
Allow approximately 1 minute for the process to complete.