how to avoid 'timer' opening a file everytime it refreshes ?

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick

        If (Process.GetProcessesByName("AcroRd32").Length > 0) Then

        End If
        Process.Start("C:\Windows\Notepad.exe")
    End Sub

When the timer runs, it opens the notepad after every 100ms or after a set interval. I want it to open only at once. How can i do that ?