custom metabox problem (PLEASE HELP ME)

hi guys i am trying to create my first custom meta box, i am not sure if this is the right place to put this but if its not, please forgive me its my first time posting too.

Ive been at this for a couple of days now and i cant figure out what i am doing wrong. i will appreciate your help, you can add or remove anything you want from my code to make it work, at this moment i will try anything really.

what the meta box suppose to do: its a very simple meta box that accepts one input field that the user will have the ability to add, delete or update client names.

here is the code:

add_action( 'init', 'create_clients' );
function create_clients(){
	register_post_type( 'clients',
		array(
			'labels' => array(
				'name' => 'Clients',
				'singular_name' => 'Client',
				'add_new' => 'Add New',
				'add_new_item' => 'Add New Clients',
				'edit' => 'Edit',
				'edit_item' => 'Edit Clients',
				'new_item' => 'New Client',
				'view' => 'View',
				'view_item' => 'View Client',
				'search_items' => 'Seach Client',
				'not_found' => 'No Client found',
				'not_found_in_trash' => 'No Client found in Trash',
				'parent_item_colon' => '',
				'menu_name' => 'Clients'
	         ),
		   'public' => true,
		   'menu_position' => 30,
		   'supports' => array(''),
		   'taxonomies' => array( '' ),
		   'menu_icon' => plugins_url('images/icon_16.png', __FILE__ ),
		   'has_archive' => true,
		   'show_in_menu' => true
		)
     );

}

add_action( 'add_meta_boxes', 'client_admin' );
function client_admin(){
	add_meta_box(
		'client_metabox_id',
		'Client Details',
		'display_clients_meta_box',
		'clients',
		'normal',
		'high'
	);
}

function display_clients_meta_box($clients){
	//print_r($clients);

    $clientName = esc_attr( get_post_meta( $clients->ID, 'display_clients', true ));
	//echo 'good';
?>
	<?php wp_nonce_field( basename( __FILE__ ), 'clients_post_class_nonce' ); ?>
    <table width="513">
        <tr>
            <td width="90"><?php _e("Client Name:"); ?></td>
            <td width="411" align="left"><input type="text" size="50" name="client_name" value="<?php echo $clientName; ?>" id="clients-post-class" /></td>
        </tr>
    </table>

<?php }

add_action( 'save_post', 'add_clients_fields', 10, 2 );
function add_clients_fields( $client_id, $clients) {

        /* Verify the nonce before proceeding. */
	if ( !isset( $_POST['clients_post_class_nonce'] ) || !wp_verify_nonce( $_POST['clients_post_class_nonce'], basename( __FILE__ ) ) )
		return $client_id;

	/* Get the post type object. */
	$post_type = get_post_type_object( $clients->post_type );

	/* Check if the current user has permission to edit the post. */
	if ( !current_user_can( $post_type->cap->edit_post, $client_id ) )
		return $client_id;

	/* Get the posted data and sanitize it for use as an HTML class. */
	$new_meta_value = ( isset( $_POST['client_name'] ) ? sanitize_html_class( $_POST['client_name'] ) : '' );

	/* Get the meta key. */
	$meta_key = 'clients_post_class';

	/* Get the meta value of the custom field key. */
	$meta_value = get_post_meta( $client_id, $meta_key, true );

	/* If a new meta value was added and there was no previous value, add it. */
	if ( $new_meta_value && '' == $meta_value )
		add_post_meta( $client_id, $meta_key, $new_meta_value, true );

	/* If the new meta value does not match the old value, update it. */
	elseif ( $new_meta_value && $new_meta_value != $meta_value )
		update_post_meta( $client_id, $meta_key, $new_meta_value );

	/* If there is no new meta value but an old value exists, delete it. */
	elseif ( '' == $new_meta_value && $meta_value )
		delete_post_meta( $client_id, $meta_key, $meta_value );

}