Private Sub Worksheet_Change(ByVal Target As Range)

    Dim rng As Range
    Set rng = Me.Range("R12")
    If Not Intersect(Target, rng) Is Nothing Then
        With Target
           If .Cells.Count > 1 Then Exit Sub
            If .Value = "" Then Exit Sub
            MsgBox "Sei sicuro di voler cancellare il contenuto della cella?"
        End With
    End If
End Sub

Sub a()
    With Application
        .OnKey "{DEL}", "messaggio"
    End With
End Sub

Sub messaggio()
MsgBox ("premuto Canc")
End Sub

Sub disabilita()
    With Application
        .OnKey "{DEL}"
    End With
End Sub

Sub a()
    With Application
        .OnKey "{DEL}", "messaggio"
    End With
End Sub
Sub messaggio()
Msg = "Vuoi veramente cancellare ?"
Style = vbYesNo + vbCritical + vbDefaultButton2
Title = "Premuto tasto Canc"
If ActiveCell.Address = "$A$4" Then
  Response = MsgBox(Msg, Style, Title)
  If Response = vbYes Then
    ActiveCell.ClearContents
  End If
Else
    ActiveCell.ClearContents
End If
End Sub

Sub disabilita()
    With Application
        .OnKey "{DEL}"
    End With
End Sub