How to get wordpress navigation to work

Question

I have been using this code to display my wordpress navigation and it worked;

<ul id="menu">
<?php wp_list_pages('sort_column=menu_order&title_li='); ?>
</ul>

However,i want to use register_nav_menus so that i can arrange my menus from the wp backend.I have this code and its not working as expected;

<?php
      wp_nav_menu( array(
    'theme_location' => 'menu',
    'fallback_cb' => 'wp_page_menu',
    )
      );
?>

My menus html should looks like this

    <ul id="menu">
    <li><a href="http://localhost">Home</a></li>

    <li>
        <a href="#">Pages</a>
    </li>
    <li>
        <a href="#">Portfolio</a>   
    </li>

    <li>
        <a href="#">Admin UI</a>    
    </li>
    <li>
        <a href="#">Features</a>    
    </li>
    <li>
        <a href="#">Shortcodes Wp 3.3</a>
                <ul>
                    <li><a href="#">Typography</a></li>
                    <li><a href="#">Sliders</a></li>
                    <li><a href="#">Columns</a></li>
                    <li><a href="#">Buttons</a></li>
                    <li><a href="#">Typography</a></li>
                    <li><a href="#">Sliders</a>
                    <ul>    
                    <li><a href="#">Typography</a></li>
                    <li><a href="#">Sliders</a></li>
                    <li><a href="#">Columns</a></li>
                    <li><a href="#">Buttons</a></li>
                    </ul>
                    </li>
                    <li><a href="#">Columns</a></li>
                </ul>               
    </li>
    <li>
        <a href="#">Blog</a>    
    </li>
    <li>
        <a href="#">Cute</a>    
    </li>
</ul>

Answer 1

Try this instead:

wp_nav_menu( array('menu' => 'Main menu' ));

Make sure you have a menu called 'Main menu'

Answer 2

I solved it this way

<?php $defaults = array( 'menu_id' => 'menu', 'echo' => true, 'fallback_cb' => 'wp_page_menu' ); ?>

 <?php wp_nav_menu( $defaults ); ?>

I was missing the 'menu_id' => 'menu' id.