Adding 'add theme support' to functions.php

Hi All.

My current functions.php file (for my own theme) looks like this:

<?php //Adding the Open Graph in the Language Attributes
function add_opengraph_doctype( $output ) {
		return $output . ' xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http://www.facebook.com/2008/fbml"';
	}
add_filter('language_attributes', 'add_opengraph_doctype');

//Lets add Open Graph Meta Info

function insert_fb_in_head() {
	global $post;
	if ( !is_single()) //if it is not a post or a page
		return;
        echo '<meta property="fb:admins" content="14412758189"/>';
        echo '<meta property="og:title" content="' . get_the_title() . '"/>';
        echo '<meta property="og:type" content="article"/>';
        echo '<meta property="og:url" content="' . get_permalink() . '"/>';
        echo '<meta property="og:description" content="' . strip_tags(get_the_excerpt()) . '"/>';
        echo '<meta property="og:site_name" content="' .  get_bloginfo('name') . '"/>';
	if(!has_post_thumbnail( $post->ID )) { //the post does not have featured image, use a default image
		$default_image="http://kylehallmusic.com/gha/wp-content/themes/gha/gha-band.jpg";
		echo '<meta property="og:image" content="' . $default_image . '"/>';
	}
	else{
		$thumbnail_src = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'medium' );
		echo '<meta property="og:image" content="' . esc_attr( $thumbnail_src[0] ) . '"/>';
	}
	echo "";
}
add_action( 'wp_head', 'insert_fb_in_head', 5 ); ?>

This is simply to get Facebook OG information.

I tried to add:

<?php add_theme_support( 'post-thumbnails' ); ?>

Underneath this to enable me to assign a default image when posting, which will put the image in the fb:image for the post.

However, this seems to break the site – when I click on the ‘like’ button, the page is blank.

Could anyone please help? Thanks…