Header Error

Everytime I try to install some plugins I get this message…

Warning: Cannot modify header information – headers already sent by (output started at /home/muslima/public_html/main/wp-content/plugins/Moody.php:35) in /home/muslima/public_html/main/wp-admin/admin.php on line 6

and I will get 4 of them with referencing lines 6, 7, 8, 9 of the admin.php file

What can I do to fix this?