I want to stop a cell in excel being left blank once user has clicked on the
cell.

I have a column that has to have a Y or N response. There is data
validation on the cell sop only Y or N can be entered. Nowever once the user
clicks on this cell i want them to HAVE to enter either the Y or N value. At
the moment if they leave it blank it accepts this as a reponse. I would like
it to force them to enter a Y or N before they can continue!