How to avoid form freezing

I'm doing a small antivirus software in VB.NET, which uses MD5 hashes to scan through the files from a computer. However, I noticed if I add more hashes into the text file which is used for the scan process, the form becomes unresponsive and crashes afterwards.

I've tried doing this through a backgroundworker, but I have no luck whatsoever. The software will use also a timer to do its work. I attached below a sample code of the timer :

ProgressBar1.Maximum = Conversions.ToString(ListBox1.Items.Count)
        total.Text = Conversions.ToString(ListBox1.Items.Count)

        If Not ProgressBar1.Value = ProgressBar1.Maximum Then
            Try

                ListBox1.SelectedIndex = ListBox1.SelectedIndex + 1
                TextBox1.Text = ListBox1.SelectedItem.ToString
            Catch ex As Exception
            End Try



            Try

                Dim scanbox As New TextBox
                Dim read As String = My.Computer.FileSystem.ReadAllText("viruslist.txt")
                ProgressBar1.Increment(1)
                Detected.Text = Conversions.ToString(ListBox2.Items.Count)
                files.Text = Conversions.ToString(ProgressBar1.Value)
                scanbox.Text = read.ToString
                Dim md5 As MD5CryptoServiceProvider = New MD5CryptoServiceProvider
                Dim f As FileStream = New FileStream(ListBox1.SelectedItem, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)
                f = New FileStream(ListBox1.SelectedItem, FileMode.Open, FileAccess.Read, FileShare.Read, 8192)
                md5.ComputeHash(f)
                Dim hash As Byte() = md5.Hash
                Dim buff As StringBuilder = New StringBuilder
                Dim hashByte As Byte
                For Each hashByte In hash
                    buff.Append(String.Format("{0:X2}", hashByte))
                Next

                If scanbox.Text.Contains(buff.ToString) Then



                    ListBox2.Items.Add(ListBox1.SelectedItem)
                End If
            Catch ex As Exception
            End Try
        Else
            Timer1.Stop()
            MsgBox("Finished Scanning Folder!")
            TabControl1.SelectTab(3)
            If ListBox1.Items.Count = 0 Then
                MsgBox("No Threats were detected, Scan Window will close!", MsgBoxStyle.Information)

            End If
        End If

I also include the code for the "Start scan" button which the user will press to begin process:

 FolderBrowserDialog1.SelectedPath = ("C:/Windows")
        FolderBrowserDialog2.SelectedPath = ("D:/")
        Try
                For Each strDir As String In System.IO.Directory.GetDirectories(FolderBrowserDialog1.SelectedPath)


                    For Each strFile As String In System.IO.Directory.GetFiles(strDir)

                    ListBox1.Items.Add(strFile)
                    total.Text = strFile
                    BackgroundWorker1.ReportProgress(strFile)
                    System.Threading.Thread.Sleep(200)

                Next

                Next


            Catch ex As Exception
        End Try

        Timer1.Start()

My problem is that if I add more MD5 hashes to the text file, the application GUI will freeze and crash. I tried preventing this situation using a backgroundWorker, however I'm not sure what needs to be changed above to fit the backgroundworker doing its job properly ? Maybe something I'm doing the wrong way? The application is made with VB.NET(Visual Studio). Any help would be greatly appreciated!