Your Chromebook may be locked in sleep mode. Please try the following procedure:
First, plug in your charger in case the battery is dead.
Push the Escape button, the Refresh button and the Power button all at the same time. They are highlighted in red in the image below.
You should see the following screen. “Please insert recovery USB” (You do not need a recovery USB)
NOTE: It may take up to a minute for the screen to show.