I've solved my problem by this way:
Edit the php.ini file:
- change extension_dir = "ext" into extension_dir = "D:\php\ext" (please write ur own path)
- change ;extension=php_mbstring.dll into extension=php_mbstring.dll (delete the ";")
- Then just save your php.ini file and copy it to ur Windows directory?(“C:\Windows“)
- restart the apache server?
The above is my solution,Hope it will work for u.