HELP Pages not working

For some reason some of my pages are no longer working. I installed Fast and Easy Checkout earlier but it seemed to work after that.

It goes to a blank page when i try
adding product to cart
clicking checkout
logging in

I looked in my cache folder for error logs and i am getting

[24-Aug-2012 23:14:06 UTC] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/familytr/public_html/includes/languages/english/ItsChristmas-1.1/header.php:33) in /home/familytr/public_html/includes/init_includes/init_templates.php on line 78
[24-Aug-2012 23:14:06 UTC] PHP Warning: session_regenerate_id() [<a href='function.session-regenerate-id'>function.session-regenerate-id</a>]: Cannot regenerate session id - headers already sent in /home/familytr/public_html/includes/functions/sessions.php on line 178
[24-Aug-2012 23:14:06 UTC] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/familytr/public_html/includes/languages/english/ItsChristmas-1.1/header.php:33) in /home/familytr/public_html/includes/functions/functions_general.php on line 45

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thanks

Somethign was wrong with my header file/ I uploaded a backup and it worked