Ajax chat has crashed my site help please

Hi installed ajax chat on mu site http://www.minkeymusic.com and it will not let me in to the back end, so cannot un install, or do very little with it, can anyone recommend the best cause of action to take with this ?

The ajax chat php file contains the following

<?php
/**
* WordPress AJAX Process Execution.
*
* @package WordPress
* @subpackage Administration
*
* @link http://codex.wordpress.org/AJAX_in_Plugins
*/

/**
* Executing AJAX process.
*
* @since 2.1.0
*/
define( ‘DOING_AJAX’, true );
define( ‘WP_ADMIN’, true );

// Require an action parameter
if ( empty( $_REQUEST[‘action’] ) )
die( ‘0’ );

/** Load WordPress Bootstrap */
require_once( dirname( dirname( __FILE__ ) ) . ‘/wp-load.php’ );

/** Load WordPress Administration APIs */
require_once( ABSPATH . ‘wp-admin/includes/admin.php’ );

/** Load Ajax Handlers for WordPress Core */
require_once( ABSPATH . ‘wp-admin/includes/ajax-actions.php’ );

@header( ‘Content-Type: text/html; charset=’ . get_option( ‘blog_charset’ ) );
@header( ‘X-Robots-Tag: noindex’ );

send_nosniff_header();

do_action( ‘admin_init’ );

$core_actions_get = array(
‘fetch-list’, ‘ajax-tag-search’, ‘wp-compression-test’, ‘imgedit-preview’, ‘oembed-cache’,
‘autocomplete-user’, ‘dashboard-widgets’, ‘logged-in’,
);

$core_actions_post = array(
‘oembed-cache’, ‘image-editor’, ‘delete-comment’, ‘delete-tag’, ‘delete-link’,
‘delete-meta’, ‘delete-post’, ‘trash-post’, ‘untrash-post’, ‘delete-page’, ‘dim-comment’,
‘add-link-category’, ‘add-tag’, ‘get-tagcloud’, ‘get-comments’, ‘replyto-comment’,
‘edit-comment’, ‘add-menu-item’, ‘add-meta’, ‘add-user’, ‘autosave’, ‘closed-postboxes’,
‘hidden-columns’, ‘update-welcome-panel’, ‘menu-get-metabox’, ‘wp-link-ajax’,
‘menu-locations-save’, ‘menu-quick-search’, ‘meta-box-order’, ‘get-permalink’,
‘sample-permalink’, ‘inline-save’, ‘inline-save-tax’, ‘find_posts’, ‘widgets-order’,
‘save-widget’, ‘set-post-thumbnail’, ‘date_format’, ‘time_format’, ‘wp-fullscreen-save-post’,
‘wp-remove-post-lock’, ‘dismiss-wp-pointer’, ‘upload-attachment’,
);

// Register core Ajax calls.
if ( ! empty( $_GET[‘action’] ) && in_array( $_GET[‘action’], $core_actions_get ) )
add_action( ‘wp_ajax_’ . $_GET[‘action’], ‘wp_ajax_’ . str_replace( ‘-‘, ‘_’, $_GET[‘action’] ), 1 );

if ( ! empty( $_POST[‘action’] ) && in_array( $_POST[‘action’], $core_actions_post ) )
add_action( ‘wp_ajax_’ . $_POST[‘action’], ‘wp_ajax_’ . str_replace( ‘-‘, ‘_’, $_POST[‘action’] ), 1 );

add_action( ‘wp_ajax_nopriv_autosave’, ‘wp_ajax_nopriv_autosave’, 1 );

if ( is_user_logged_in() )
do_action( ‘wp_ajax_’ . $_REQUEST[‘action’] ); // Authenticated actions
else
do_action( ‘wp_ajax_nopriv_’ . $_REQUEST[‘action’] ); // Non-admin actions

// Default status
die( ‘0’ );

I stupidly just installed it and activated it
Any help appreciated