Warning: require_once ???

Hi, yesterday morning my website http://www.lefemi.com was working and then, in the afternoon, I am finding this message :
Warning: require_once(/homepages/21/d223868024/htdocs/femi/wp-includes/template-loader.php) [function.require-once]: failed to open stream: No such file or directory in /homepages/21/d223868024/htdocs/femi/wp-blog-header.php on line 19

Fatal error: require_once() [function.require]: Failed opening required ‘/homepages/21/d223868024/htdocs/femi/wp-includes/template-loader.php’ (include_path=’.:/usr/lib/php5.2′) in /homepages/21/d223868024/htdocs/femi/wp-blog-header.php on line 19

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On line 19, there is what I have :

require_once( ABSPATH . WPINC . ‘/template-loader.php’ );

—————–

in my wp-admin, I have this error message :

Warning: Cannot modify header information – headers already sent by (output started at /homepages/21/d223868024/htdocs/femi/wp-includes/functions.php:3783) in /homepages/21/d223868024/htdocs/femi/wp-includes/option.php on line 828

Warning: Cannot modify header information – headers already sent by (output started at /homepages/21/d223868024/htdocs/femi/wp-includes/functions.php:3783) in /homepages/21/d223868024/htdocs/femi/wp-includes/option.php on line 829

on line 828 and 829, there is what I have :
setcookie( ‘wp-settings-‘ . $user_id, $settings, time() + YEAR_IN_SECONDS, SITECOOKIEPATH, null, $secure );
setcookie( ‘wp-settings-time-‘ . $user_id, time(), time() + YEAR_IN_SECONDS, SITECOOKIEPATH, null, $secure );

Do you know, where is my mistake please ?