Two things to try that will take care of most Chromebook issues:

Quick Reset 

This will take care of many Chromebook issues.  Hold down the refresh and the power key.  It will shut down the Chromebook and power it up. It takes about 15 seconds.

Powerwash 

If the quick reset does not take care of the issue, the powerwash probably will.  The powerwash takes about 2 minutes.