WWW.domain.com Doesn't Work

Please help. My site, http://workflowcreative.com works great without the www, but add it in and the site goes blank: http://www.workflowcreative.com .

Here’s what I’ve already tried.

• Happens with Twenty-Eleven theme
• Happens with all plugins disabled
• Happens even if I add
  define(‘WP_HOME’, ‘http://workflowcreative.com’); // blog url
  define(‘WP_SITEURL’, ‘http://workflowcreative.com’); // site url
  to wp-config.php
• If I add
  define(‘WP_HOME’, ‘http://www.workflowcreative.com’); // blog url
  define(‘WP_SITEURL’, ‘http://www.workflowcreative.com’); // site url
  then ONLY the WWW address works and the version without WWW goes to a blank page.
• Adding the following to .htaccess doesn’t fix it either:
  Options +FollowSymlinks
  RewriteEngine on
  RewriteCond %{HTTP_HOST} !^www\.workflowcreative\.com
  RewriteRule ^(.*)$ http://workflowcreative.com/$1 [R=301,L]
• If I delete WordPress off the site then the domain works with and without the WWW.

Help! Please! I’m trying to run a contest on the site to give away an iPad Mini, but people who try to access it with http://www.workflowcreative.com are not getting through.