Subdomains

My blog is at brentirwin.tv. I used WordPress a second time at “subdomain”.brentirwin.tv as a blog for something else. The problem is, when I try going to “subdomain”.brentirwin.tv/wp-admin/install.php like you are supposed to do to when you install a new blog, it says that it has already been installed. I then click on the link it gives me and sends me to brentirwin.tv. How do I get WordPress to work a second time here?