*Second one tonight, if there's a third I may want to buy a lottery ticket...*
Give this a read regarding the "headers already sent" message.
It's often your wp-config.php file, but in your case I think it's the wp-content/themes/magazine-basic/functions.php file.
You can download a fresh copy for that theme and using FTP or whatever file management tools your host has provided you with transfer a clean copy of the `theme on top of the one that is giving you a problem.
http://wordpress.org/extend/themes/magazine-basic
http://wordpress.org/extend/themes/download/magazine-basic.2.7.9.zip
Your site has Magazine Basic 2.7.7 and you will lose any changes you made but uploading the newer files should be alright. if you are unsure then make a backup copy of the current magazine-basic directory first.