こんなのでやって見てください。
Private Sub Worksheet_Change(ByVal Target As Range)
Dim cel As Range
If Intersect(Target, Columns("D:E"), Me.UsedRange) Is Nothing Then
Exit Sub
Else
For Each cel In Target
If Cells(cel.Row, "A") <> Empty Then '同行のA列に何か入っている場合のみ処理
If Cells(cel.Row, "D") = "" And Cells(cel.Row, "E") = "" Then
Application.EnableEvents = False
Cells(cel.Row, "A") = Empty
Application.EnableEvents = True
End If
End If
Next
End If
End Sub