There is a catch when installing Xdebug on windows: You need to set the full path of the extension directive in the php.ini, since the default directory is only used for non-zend extensions. Also don’t forget to use quotes.
;used only for 'normal' extensions extension_dir = "C:Program Files (x86)PHPext" ;still necessary to use full path zend_extension = "C:Program Files (x86)PHPextphp_xdebug.dll" ;won't work ;zend_extension = php_xdebug.dll
To make Xdebug work in PhpStorm you also need to enable remote debugging:
xdebug.remote_enable = 1