If you are having trouble your Chromebook, many issues can be resolved with a hard reset.  To do a hard reset of your Chromebook, press the Power and the Refresh keys at the same time for 10 seconds. The keyboard picture below shows you the location of those keys.

To capture a full screenshot, hold down the "ctrl" key and the "switch window" key (pictured below) at the same time.

To capture a partial screenshot, hold down the "ctrl," "shift," and "switch window" keys at the same time.