For your site type in "www.yoursitename.com".  Look in the address bar where your site name is:

browserbar

Is the "www" still there?  Now, type in "yoursitename.com" without the "www".  Check again for the "www".

 

You want your website to either resolve to www.yoursitename.com or yoursitename.com - regardless of whether or not "www" is entered. This is called your Preferred domain name. This is important for your search engine results.

You can use a 301 redirect to redirect traffic from your non-preferred domain name or on Joomla sites which we develop, we commonly take care of this in the .htaccess file.