macro to trigger Cond Formatting when just CLICK on any cell in a range

Hi

i'm trying to write a macro that will trigger the Conditional Formatting when I just CLICK on any cell within the specified range, but it doesn't seem to be working. Can anyone who knows where I'm wrong/inadequate point me in the right way here..?

Private Sub Worksheet_Change(ByVal Target As Range)

   If Selection.Count = 1 Then
        If Not Intersect(Target, Range("A2:Q1000")) Is Nothing Then
        Range("A2:Q1000").FormatConditions(1).StopIfTrue = True
        ActiveSheet.Calculate
        End If
   End If

End Sub

cheers
Stewart