header already loaded?? Can't login

I get this when I try to login- I have already tried to reset using the WP-CONFIG-Sample.php I get this message when i do.

Warning: Cannot modify header information – headers already sent by (output started at /mnt/vhosts/theageofgifts.com/httpdocs/wp-content/themes/wp-creativix/functions.php:8) in /mnt/vhosts/mywebsite.com/httpdocs/wp-includes/pluggable.php on line 890