Try Like This:
Below is code snippet how to list all directories & sub-directories in vb.net (ASP.net)
imports system.IO namespace
Dim filepath As String = String.Empty
If (Directory.Exists("c:\")) Then
Dim drInfo As DirectoryInfo = New DirectoryInfo(folderpath)
Dim files() As FileInfo = drInfo.GetFiles("*.opf")
If (files.Length > 0) Then
filepath = files(0).FullName
End If
End If