Since you havent posted any code i wont give you the whole solution.
What you need to do is to use recursion.
Write a method/function that calls itself like this.
void recursive_method(string Folder_To_Browse)
System.IO.DirectoryInfo DI = new System.IO.DirectoryInfo(Folder_To_Browse);
foreach(System.IO.DirectoryInfo sub_folder in DI.GetDirectories())
This was written on the top of my head so it might contain errors.
But it should help get you started.