File is not shown in OpenFileDialog - vb.net

Question

I'm trying to do something like a text editor in VB 2012, so I have a MenuStrip with an "OpenFile" option. When it's clicked it fires an OpenFileDialog control and shows me just the files with the extension I want. The problem is that if I close the file with another option in the menu strip, when I want to open the same file I opened the first time using the same OpenFile option the OpenFileDialog is not showing me the file.
Do you know why is that?
Here is how I open the file:
Private Sub OpenFileToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles OpenFileToolStripMenuItem.Click
'Open File
If OpenFile.ShowDialog() = Windows.Forms.DialogResult.OK Then
If Not (OpenFile.FileName = "") And OpenFile.CheckFileExists Then
NewFile = New StreamReader(OpenFile.FileName)
If NewFile IsNot Nothing Then
Me.TextBox_Main.Text = NewFile.ReadToEnd
Me.TabPage1.Text = OpenFile.FileName.Substring(OpenFile.FileName.LastIndexOf("\") + 1)
End If
End If
End If
End Sub
And here is how I close the file:
Private Sub CloseFileToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles CloseFileToolStripMenuItem.Click
'Close Files
If NewFile IsNot Nothing Then
NewFile.Close()
NewFile = Nothing
End If
Me.TextBox_Main.Text = ""
Me.TabPage1.Text = "New Tab"
End Sub