I cannot access my dashboard with my username and password

Hi, Whenever I try to access my Dashboard the following message comes up:

Warning: Cannot modify header information – headers already sent by (output started at /var/www/vhost/cesaregido.com/home/html/wp-config.php:1) in /var/www/vhost/cesaregido.com/home/html/wp-includes/pluggable.php on line 890

And I don′t know what this is. Please help!!!