I have installed PHP and MySQL and I can see only blank page. What's wrong?

MySQL is not enabled by default, nor is the MySQL library bundled with PHP. In order to have these functions available, you must compile PHP with MySQL support.
PHP manual - MySQL

Set conf['debug_info'] = 1 in your_kb_installation_directory/admin/config.inc.php. It will  display  an error if  you do not have MySQL extension enabled.