Something doesn't appear to be installed correctly; I was able to get it to start serving the actual forum by moving index.html to index.html.bak (our server is set up that if there's an index.html and an index.php, like there is in your case, it will serve the html file first, when in your case it actually needed to serve the php file first).
Once I fixed that however, the forum does load, but everything appears to be broken - the theme doesn't appear to be loading at all. I would recommend going back through the install directions once again to ensure you're not missing anything (in particular, was it supposed to come with a .htaccess file that might fix this).