Warning: require_once(__DIR__/wp-load.php) [function.require-once]: failed to open stream: No such file or directory in C:\Apache_Site\wp-blog-header.php on line 13

Fatal error: require_once() [function.require]: Failed opening required '__DIR__/wp-load.php' (include_path='.;C:\php5\pear') in C:\Apache_Site\wp-blog-header.php on line 13