Hello, plss help me.

I started a project, an explorer aplication. I use a form and two classes for the treeview and listview objects. The listview class works ok, but the treeview class has a bug. At startup i declared it to fill with the contents of the computer, but I cannot access those folders.
My treeview class is called "DirectoryTreeView"
When I wanna acces it I call the variable: "Private dtvwDirectory As DirectoryTreeView" but all the time I get an error like this "Object reference not set to an instance of an object." If I use "Private dtvwDirectory As New DirectoryTreeView", the new class will be empty.
Ideeas?

Do you know any explorer projects?
Thx