Cycle through sub-folders and files in a user-specified root directory [duplicate]

My cycling script through individual files works fine, but I now need it to also look through/for multiple directories. I am stuck....

The order things need to happen:

• User is prompted to choose root directory of what they need
• I need the script to look for any folders in that root directory
• If the script finds one, it opens the first one (all folders, so no specific search filter for the folders)
• Once open, my script will loop through all files in the folders and do what it needs to do
• after it's finished it closes the file, closes the directory and moves to the next one, etc..
• Loops until all folders have been opened/scanned

This is what I have, which doesn't work and I know is wrong:

MsgBox "Please choose the folder."
Application.DisplayAlerts = False
With Application.FileDialog(msoFileDialogFolderPicker)
    .InitialFileName = "\\blah\test\"
    .AllowMultiSelect = False
    If .Show <> -1 Then MsgBox "No folder selected! Exiting script.": Exit Sub
    CSRootDir = .SelectedItems(1)
End With
folderPath = Dir(CSRootDir, "\*")

Do While Len(folderPath) > 0
    Debug.Print folderPath
    fileName = Dir(folderPath & "*.xls")
    If folderPath <> "False" Then
        Do While fileName <> ""
            Application.ScreenUpdating = False
            Set wbkCS = Workbooks.Open(folderPath & fileName)

            --file loop scripts here

        Loop  'back to the Do
Loop    'back to the Do

Final Code. It cycles through all sub-directories and files in each sub-directory.

Dim FSO As Object, fld As Object, Fil As Object
Dim fsoFile As Object 
Dim fsoFol As Object 
Dim fileName As String

    MsgBox "Please choose the folder."
    Application.DisplayAlerts = False
    With Application.FileDialog(msoFileDialogFolderPicker)
         .InitialFileName = "\\blah\test\"
         .AllowMultiSelect = False
         If .Show <> -1 Then MsgBox "No folder selected! Exiting script.": Exit Sub
         folderPath = .SelectedItems(1)
    End With

    If Right(folderPath, 1) <> "\" Then folderPath = folderPath + "\"
         Set FSO = CreateObject("Scripting.FileSystemObject")
         Set fld = FSO.getfolder(folderPath)
    If FSO.folderExists(fld) Then
         For Each fsoFol In FSO.getfolder(folderPath).subfolders
              For Each fsoFile In fsoFol.Files
                   If Mid(fsoFile.Name, InStrRev(fsoFile.Name, ".") + 1) = "xls" Then
    fileName = fsoFile.Name
    Application.ScreenUpdating = False
    Set wbkCS = Workbooks.Open(fsoFile.Path)

    'My file handling code


                End If
              Next
         Next
    End If