In order to configure Zen Cart to work properly with another domain, you should modify the two configure.php files in includes/ and admin/includes/ folders to reflect the new domain.

The settings that should be changed in includes/configure.php are:

HTTP_SERVER - you should change this to your new domain name, e.g. http://newdomain.com:

define('HTTP_SERVER', 'http://newdomain.com');

If you are using SSL you should also modify:

HTTPS_SERVER - change this to:

define('HTTPS_SERVER', 'https://newdomain.com');

In admin/includes/configure.php you should modify:

HTTP_SERVER - you should change this to your new domain name, e.g. http://newdomain.com:

define('HTTP_SERVER', 'http://newdomain.com');

HTTP_CATALOG_SERVER - again, this should be changed to your new domain name:

define('HTTP_CATALOG_SERVER', 'http://newdomain.com');

If you are using SSL, you should also change:

HTTPS_SERVER - change this to:

define('HTTPS_SERVER', 'https://newdomain.com');

HTTPS_CATALOG_SERVER - change this to:

define('HTTPS_CATALOG_SERVER', 'https://newdomain.com');