I guess your WordPress is installed in folder blog
and when changing the site url to http://user99.com WP lost its actual path. So if can access wp-config.php and add the following two line your issue should be solved.
define('WP_HOME''WP_SITEURL','http://user99.com');
define('WP_SITEURL''WP_HOME','http://user99.com/blog');
EDIT As Frank P. Walentynowicz corrected me this will permanently change your addresses and the standard WP settings for site url and home url will be disabled so it is better to use Frank's method for editing the Database.