changing non-www to www is not working

I need some help please, before I pull out all of my hair…

I decided to move my blog from Typepad to WordPress. I first installed with Fantastico and could only set the blog up as non-www sub-domain (blog.brandsproutmarketing.com). I read that the problem might be Fantastico, so I uninstalled and did a manual install.

After several hours, I still cannot get the blog working with the URL http://www.blog.brandsproutmarketing.com. I’ve tried changing the URLs in options_general, but I immediately get booted out of the wp admin with a 404 broken link error, which appears for BOTH www and non-www addresses.

The only way I can get back into wp is to manually edit the site URL in the wp_options table of the database to remove the www.

Previously (with Typepad) I had a redirect set-up to send the non-www URL to the www URL, which worked just fine. I have removed this redirect from my site, and deleted the htaccess file so there are no active redirects messing things up, but I can’t seem to get around this issue.