Помогите с установкой

Undefined index: user
Error on file /var/www/u4835975/public_html/stats/function/auth.php, on line: 200

Code: $sql = sprintf("SELECT * FROM `users` WHERE %s = '%s'", $col, $_COOKIE[$col] );
Undefined index: user
Error on file /var/www/u4835975/public_html/stats/function/auth.php, on line: 211

Code: if ( $row[$col] !== $_COOKIE[$col] || $row['password'] !== $_COOKIE['password'] || $row['prefix'] != $db->prefix ) {
Cannot modify header information - headers already sent by (output started at /var/www/u4835975/public_html/stats/including/check.php:95)
Error on file /var/www/u4835975/public_html/stats/function/auth.php, on line: 165

Code: setcookie($name, '', time()-1, '/');
Cannot modify header information - headers already sent by (output started at /var/www/u4835975/public_html/stats/including/check.php:95)
Error on file /var/www/u4835975/public_html/stats/function/auth.php, on line: 165

Code: setcookie($name, '', time()-1, '/');
Cannot modify header information - headers already sent by (output started at /var/www/u4835975/public_html/stats/including/check.php:95)
Error on file /var/www/u4835975/public_html/stats/function/auth.php, on line: 165

Code: setcookie($name, '', time()-1, '/');
Cannot modify header information - headers already sent by (output started at /var/www/u4835975/public_html/stats/including/check.php:95)
Error on file /var/www/u4835975/public_html/stats/function/auth.php, on line: 185

Code: header('Location: '.$_SERVER['PHP_SELF'].$multi_get);

Что за проблема?