.htaccess with subdomain non-www to www

I understand the basics of non-www to www versions of a website through the htaccess but what normally works isn’t working in this case.

Here’s what’s happening:

-http://sub.domain.com is working fine
-http://www.sub.domain.com – returns a “Website Suggestions” screen.

How do I get this to work correctly? I’ve tried 3 or 4 different non-www to www htaccess tactics. If it matters this website is on GoDaddy servers.

Here’s what I’m currently using

# protect the htaccess file
<files .htaccess>
order allow,deny
deny from all
</files>

# protect wpconfig.php
<files wp-config.php>
order allow,deny
deny from all
</files>

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteBase /
rewritecond %{http_host} ^DOMAIN-NAME [nc]
rewriterule ^(.*)$ http://www.sub.domain.com/$1 [r=301,nc]
</IfModule>

# END WordPress