New installation not working

Hi

I am trying to install piwik on our web server and am running up against erros in the php config re adding extensions:

extension=php_mysqli.dll
extension=php_pdo.dll
extension=php_pdo_mysql.dll

and mbstring. these have all been added to the php.ini file and web server restarted but the piwik installation is still complaining that they are not there. i’m not sure what i am doing wrong. has anyone got any ideas?

Many thanks

Stewart