Can’t access wp-admin for my blog–please help

I uploaded a new theme and have been working on modifying it. I uploaded a new header (header.jpg) via FTP, and it replaced the existing header with not problem.

When I tried to access the dashboard, however, I receive the following error:

Warning: Cannot modify header information – headers already sent by (output started at /webroot/w/e/webbe004/www/blog/wp-content/themes/oceanblue-20/functions.php:7) in /webroot/w/e/webbe004/www/blog/wp-admin/theme-editor.php on line 55

In IE, of all browsers, I can access the dashboard, but everytime I save a change, I get an error like the one listed above. In the URL, if I remove everything after wp-admin, I can get back in. This only works in IE, however. I can’t access the backend of the blog using FF for the PC, FF for a Mac, or Safari for the Mac.

My blog is at: https://www.web-betty.com/blog/

Thanks!

Melissa