right-click on your sheet tab, choose view code, paste the procedures below...
<pre>
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column = 1 Then
If Target.Value > 500 Then
BlinkBlink Sheet1.Range("A" & Target.Row)
End If
Columns(1).Interior.ColorIndex = 0
End If
End Sub
Sub BlinkBlink(BlinkingRange As Range)
Dim Start
Do Until BlinkingRange.Value <= 500
Start = Timer
Do While Timer < Start + 1
If Timer = 0 Then Start = Timer
DoEvents
Loop
If BlinkingRange.Interior.ColorIndex = 3 Then
BlinkingRange.Interior.ColorIndex = 0
Else: BlinkingRange.Interior.ColorIndex = 3
End If
Loop
End Sub
</pre>