ASP.Net Masterpage and navigation menu

I am using a master page in my new project, header at the top, navigation menu on the left and content page on the right.

I have one sub menu which adds a new employee's data and will navigate to content page if you click.

My problem is I want the user to fill all the info first and only the Save and Cancel button are enabled, and should not able to click anywhere and page especially the navigation menu.

I am using a treeview on my navigation menu.