How to go back to the Main Window in WPF(Navigation Service)

Good Day All

I have a Kinect Application , i am having trouble with navigation , so i dont like the creation of object of windows everytime i nagivate from one to another page. so i converted all other windows to WPF pages and created only one window wich will be the Startup screen where Navigation will begin. So Other windows might also contain Menu's so to cut the story short , i can nagivate between WPF pages and do anything i want. but i want to be able to go to the Main Page(Window) which has the Menus. Which means i am trying to navigate from a Page to a Window.

Main Window has the Frame

Code:

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              <DockPanel>
                    <Frame x:Name="_mainFrame" />
                </DockPanel>

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and i cna navigate to the pages with no problems and between them , but when i want to go to the main Window from a Page i cant.