Trouble creating blog directory

Hi,

I am using WordPress as a CMS for a friend’s site (www.dawnnelson.org).

It works great!

Now, we want to start a blog.

Under General Settings, I have both the blog and the WordPress URLs as https://www.dawnnelson.org.

I have tried changing the blog address to both blog.dawnnelson.org and dawnnelson.org/blog, but neither one works.

It ends up breaking the theme of the site until I go back and change both URLs to the root.

Does anyone know what I am doing wrong when I try to set up the blog?

Thanks,
Josh