Please Help – Have I broken it?

I’ve been trying to make some changes to http://www.essexmums.org/naming/ as the plugin I was using to randomise posts seems to have stopped working.

I found something that suggested adding this:

<?php
add_action( 'pre_get_posts', 'random_posts' );

function random_posts( $query ) {
	if ( $query->is_home() && !$query->is_paged() && $query->is_main_query() ) {
		$query->set( 'orderby', 'rand' );
	}
}

to the functions.php file, so tried that and now everything has gone blank. I can navigate back to the functions.php file, but when I removed the new code it changed nothing. I can’t see anything on the page, nor can I log in.

is there anything I can do to save this?