Private Sub Worksheet_Change(byval target as range)

    If Not Intersect(target.address = Range("YourCells")) is Nothing Then
       MyMacro()
    End If

End Sub

Private Sub Worksheet_Change(byval target as range)

    If target.address = Range("YourCell").Address Then Application.Calculate

End Sub

Private Sub Worksheet_Activate

Application.Calculation = xlCalculationManual

End Sub

Private Sub Worksheet_Deactivate

Application.Calculation = xlCalculationAutomatic

End Sub