After install if you see the admin login page but it is not working it is usually because the cms_root_url is not being automatically set correctly. If you go to scripts/config.php you can set the cms_root_url manually - to do this make sure the line is uncommented by removing any forwardslashes and enter the url to your root folder where the cms installed.
//define('cms_root_dir','');
define('cms_root_url','http://www.mysite.com/cms/');