the little square at the bottom of a cell in excel not working

Display or hide the fill handle

The fill handle Selected cell with fill handle is displayed by default, but you can turn it on or off.
  1. Click the Microsoft Office Button Button image, and then click Excel Options.

  1. In the Advanced category, under Editing options, select or clear the Enable fill handle and cell drag-and-drop check box to display or hide the fill handle.