Instructions
Press the guide button--the large X in the middle of the controller--so that the menu comes up. Once it is available, press the blue X to open a new dialog window, then select "Yes" to end your Xbox session.
Hold down the Guide button again until a new window with different options appears.
Choose "Turn off controller." There will be an option to turn off the controller and the console, but you need to avoid this to reset the system.
Press the start button to the right of the Guide button. This should turn your controller back on, completing the reset process.