C# [FIXED] prevent richtextbox from displaying the same string after the second time run

Code
   private void Display(string text, bool newLine = true)

    {

        DisplayTextBox.AppendText(text);

        if (newLine)

        {

            DisplayTextBox.AppendText(Environment.NewLine);

            DisplayTextBox.ScrollToCaret();

        }

    }



        private void startScan()

        {

            Display("...........................................................................................", true);

            Display("[ " + DateTime.Now.ToLongTimeString() + " ] - [ # ] Starting scanning, please wait . . . . . .", true);

            Display("...........................................................................................", true);

            Display(Environment.NewLine, true);

            Thread.Sleep(100);

            this.DirButton.Enabled = false;

            this.ScanButton.Enabled = false;

            scanned = 0;

            skipped = 0;

            worker.WorkerReportsProgress = true;

            worker.DoWork += Scan;

            worker.ProgressChanged += this.ProgressChanged;

            worker.RunWorkerCompleted += this.RunWorkerCompleted;

            worker.RunWorkerAsync();

        }



        private static void Scan(object sender, DoWorkEventArgs e)

        {

            startScan(e.Argument.ToString());

        }



        private void ProgressChanged(object sender, ProgressChangedEventArgs e)

        {

            Display(e.UserState.ToString(), true);   

        }



        private void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)

        {

            if (e.Error != null)

            {

                this.Display("[ " + DateTime.Now.ToLongTimeString() + " ] - [ ! ] Exception: " + e.Error.ToString(), true);

            }

            if (!e.Cancelled)

            {

                string text = "[ " + DateTime.Now.ToLongTimeString() + " ] - Scanned [ " + scanned + " ] files ";

                string text2 = "[ " + DateTime.Now.ToLongTimeString() + " ] - Skipped [ " + skipped + " ] files ";

                Display(Environment.NewLine,true);

                Display("--------------------------------------------------------------------------------------", true);

                Display("[ " + DateTime.Now.ToLongTimeString() + " ] - [ √ ] Finished.", true);

                Display("--------------------------------------------------------------------------------------", true);

                Thread.Sleep(100);

                if (Form1.skipped > 0)

                {

                    Display(text2,true);

                }



                else if (Form1.skipped == 0)

                {

                    Display(text2,true);

                }



                this.Display(text,true);

                Display("--------------------------------------------------------------------------------------", true);

                Thread.Sleep(100);

                DirButton.Enabled = true;

                ScanButton.Enabled = true;

                return;

            }

            Display("[ " + DateTime.Now.ToLongTimeString() + " ] - [ x ] Scanning cancelled", true);

            DirButton.Enabled = true;

            ScanButton.Enabled = true;

        }



    private static int scanned = 0;

    private static int skipped = 0;

    private static BackgroundWorker worker = new BackgroundWorker();