Layer Mask and Brushing in Elements 18

When I add a layer mask to an image, I cannot get the brush tools to work.  When I select the brush tool in black or white I cannot erase or restore the image.  I move the brush along the image, but nothing appears on the layer mask documenting the action.  Nothing changes with the appearance of the image.  Opacity is at 100%.  The layer mask is selected with the blue border.  I would greatly appreciate any help or guidance.  I'm very frustrated!  Thanks in advance!