Menu not showing up

When I create a menu and then add the menu to the Theme location, it is not showing up on the page. I view the page and still get the text ‘Please attach a menu to this menu location in Appearance > Menu.’ Then, when I go back to Appearance/menus/manage locations, it again shows -Select a Menu- like I never chose a menu selection. It constantly reverts my change and I can never get the menu to show up.