Need help

Hello,
Below is the error comes out when I tried to view the theme on the browser via admin panel, appearance, theme after paste the Yootheme folder in the wordpress>wp-content>themes>

Fatal error: Call to undefined function register_nav_menus() in C:\wamp\www\wordpress\wp-content\themes\yoo_air\yoo_air_wp\warp\systems\wordpress.3.0\helpers\system.php on line 154

That theme crashed my wordpress site very badly.

Now I cannot able to access both admin panel and front view.

How can I make it back because I do have necessary information in the site and I do not want to reinstall the whole package again.

I forget the version of wordpress too which I installed in my system.

Kindly let me know how I can be able to recover my wordpress site again.

SABA