Menu Invisible

Hi Guys,
Can anyone help – My menu somewhere along the line vanished.
I have deactivated ALL plugins, to no avail and switched to default theme, where the menu displays as it should – switched back and menu is not visible.

This is all I can see that relates to Navigation, that exists in the presented html page:

<nav id="access">
	<a class="nav-show" href="#access">Show Navigation</a>
	<a class="nav-hide" href="#nogo">Hide Navigation</a>
	<div class="clear"></div>
</nav><!-- #access -->

There should be three or four top menu items, each with multiple submenus.

Any help appreciated!