Safe Mode puts your phone in a diagnostic state (returned to default settings) so you can determine if a third-party app is causing your device to freeze, reset or run slow.
An alternate method is available if the device is unresponsive or won't power on.
With the device powered on, press and hold the Power button (located on the upper-right edge) until the Tablet options prompt appears then release.
Touch and hold Power off until "Reboot to safe mode" appears then tap OK.
The restart process may take up to 45 seconds to complete.
Upon restart, Safe mode appears in the lower left of the unlock/home screen.