Directional light not light floor

I have a student’s project with lighting issue. His environment is a cube with 6 walls all identical settings. The 4 used for vertical walls and the ceiling work but the floor will not light. I am attaching a screen shot of the room, also the Inspector for light and one wall (they are all identical). Can’t figure out how to attach the game package. Any help would be greatly appreciated!

HELP!!! Can anyone help me with this???