WordPress 3.5 Add New Media Not Working Solution: The New WordPress 3.5 Version has many issues and most of users are creating threads at wordpress support forum.
I had also faced this problem and fixed in the following way. So Here is the simple solution.
Login to your cPanel and browse ftp folder. Now Open “wp-config.php” file with “Code Editor” and Scroll Down at the bottom of the file. Here you will see this line : require_once(ABSPATH . ‘wp-settings.php’);
Just add: define(‘CONCATENATE_SCRIPTS’, false ); right before the above line. Save the file.
Thats it. Done.
I hope it works for you.