code stops working when i put a formula in the cell

[Sarangsood]

the following code works well for me but when i put a formula in A1 or link it from somewhere it stops working

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address <> "$A$1" Then Exit Sub
Range("B65536").End(xlUp).Offset(1, 0).Value = Target
Range("C65536").End(xlUp).Offset(1, 0).Value = Format(Now(), "mm/dd/yy" & " " & "hh:mm:ss")
End Sub

plz help me convert this code