Are you trying to install it together with the content that already is in your root, ie the content/site I see in the url you gave us?
If so, that might be the problem, I believe you can only have one index page in each folder, this case the root.
I would create the blog in a subfolder/subdomain and then either link to it from the site or when move the blog from the subfolder to the root (if you want to replace the current content with the blog that is).