Whats wrong with my filesystem watcher code VB.NET

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VB

anti-virus

when my file system watcher detects a virus a dialog shows but when i click the delete file option it says its open in my program but in the filesystem watcher when i add the openfiledialog.Dispose function it doesnt show my dialog so heres the code can somone provide a fix? code below.

Private Sub FileSystemWatcher1_Changed(ByVal sender As System.Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed
        Try
            Detect.Labellastreal.Text = e.FullPath
            ListBox3.Items.Add(Detect.Labellastreal.Text)
            Me.OpenFileDialog3.FileName = ""
            Dim scanbox As New TextBox
            scanbox.Text = My.Computer.FileSystem.ReadAllText(Application.StartupPath & "\VirusList.dat").ToString
            Dim md5 As New MD5CryptoServiceProvider
            Dim f As New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, &H2000)
            f = New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, &H2000)
            md5.ComputeHash(f)
            Dim hash As Byte() = md5.Hash
            Dim buff As New StringBuilder
            Dim hashByte As Byte
            For Each hashByte In hash
                buff.Append(String.Format("{0:X2}", hashByte))
            Next
            f.Close()
            If scanbox.Text.Contains(buff.ToString) Then
                Me.OpenFileDialog3.FileName = e.FullPath
                Detect.ShowDialog()


                WriteToLog("Virus detected")

            End If

        Catch exception1 As Exception
            ProjectData.SetProjectError(exception1)
            Dim ex As Exception = exception1
            ProjectData.ClearProjectError()
        End Try
    End Sub

What I have tried:

i said in the first one that i tried OpenFileDialog.Dispose method but didnt work :(
can someone please provide a fix thanks in advance.