Make a macro in the Workbook_BeforeClose(), which checks if the user put some
data in cell A1. If none it puts a messagebox on the screen then it cancels
the closure of the workbook, until the user has put some data in A1. Here is
the code:
Private Sub Workbook_BeforeClose(Cancel As Boolean)
If IsEmpty(Range("A1")) Then
MsgBox "Please enter data in A1."
Cancel = True
End If
End Sub

Swisse