Login Issue

Hi, I was wondering if anyone could help me out? I run a blog- http://moonraito.sailormoon.cc/ which I haven’t had any problems until now.

When ever I go to my login page- http://moonratio.sailormoon.cc/wp-admin/ I keep getting this error-

Warning: Cannot modify header information – headers already sent by (output started at /homepages/12/d212162477/htdocs/moonratio/wp-settings.php:96) in /homepages/12/d212162477/htdocs/moonratio/wp-includes/pluggable.php on line 890

But I can not access the site to see what the problem is. At first my co-helper thought it was wordpress itself and he thinks he need to delete it and re-install it. I have no idea. The site|blog works fine, but we can not log in to make any changes or updates.

If anyone on here can help out that would be great. If you could reply back to my email-[redacted] that would be great. Thanks so much,
~Lilly-chan