Sem acesso ai painel do WP

Conseguir fazer tudo direitinho mas não estou conseguindo acesso ao painel nem a modificação nenhuma. Quando vou na tela de login, ponho o usuário e a senha daí aparece essa mensagem:

Warning: Cannot modify header information – headers already sent by (output started at /home/arquiban/public_html/wp-config.php:1) in /home/arquiban/public_html/wp-login.php on line 349

Warning: Cannot modify header information – headers already sent by (output started at /home/arquiban/public_html/wp-config.php:1) in /home/arquiban/public_html/wp-login.php on line 361

Warning: Cannot modify header information – headers already sent by (output started at /home/arquiban/public_html/wp-config.php:1) in /home/arquiban/public_html/wp-includes/pluggable.php on line 669

Warning: Cannot modify header information – headers already sent by (output started at /home/arquiban/public_html/wp-config.php:1) in /home/arquiban/public_html/wp-includes/pluggable.php on line 670

Warning: Cannot modify header information – headers already sent by (output started at /home/arquiban/public_html/wp-config.php:1) in /home/arquiban/public_html/wp-includes/pluggable.php on line 671

Warning: Cannot modify header information – headers already sent by (output started at /home/arquiban/public_html/wp-config.php:1) in /home/arquiban/public_html/wp-includes/pluggable.php on line 866

Caso alguém possa me ajudar, obrigado desde já.