mysqli.dll没有加载，虽然存在于PHP文件夹中

I run a php script on Apache 2.4 on Windows 7 which loads library mysqli. The function extension_loaded('mysqli') returns false.

My php.ini includes lines:

extension_dir = "ext"
extension=php_mysqli.dll

and in {$PHProot}/ext directory there is indeed aforementioned file. The file mysqli.dll is in MySQL Server Folder and I copied it also to php root directory and into {$PHProot}/ext.

EDITS:

According to phpinfo(), correct (above referenced) php.ini is used, but no modules were loaded

Any suggestions, what my cause this?

Thanks, Zbynek