Admin panel error

My site is http://www.vistarewired.com

Might you guys know why I am getting this error?
Warning: Cannot modify header information – headers already sent by (output started at /home/vistarw1/public_html/wp-config.php:27) in /home/vistarw1/public_html/wp-includes/pluggable.php on line 275

thanks for ur help =) btw my webhosting company told me to:
define(‘DISABLE_CACHE’, true);

then this happened