Well go to your php.ini and check that it looks like below:
;extension=php_maxdb.dll
extension=php_mbstring.dll
Note that the semicolon has been removed. multibyte string is disabled by default with PHP you must enable it yourself. From the Manual :
Installation
mbstring is a non-default extension. This means it is not enabled by default. You must explicitly enable the module with the configure option. See the Install section for details.