Cannot access admin panel dashboard

I am newbie, and have not kwowingly changed anything, but now when I go to barbaramilne.com/wp-admin/index.php to login, i get this message. Website shows up when you go to http://www.barbaramilne.com, but when someone tries to order or contact me or anything, there is no way. This error code below shows up. HELP

Warning: require_once(/home/barbara/public_html/wp-content/themes/woostore/functions/classes/class-wp-app-store-installer.php) [function.require-once]: failed to open stream: No such file or directory in /home/barbara/public_html/wp-content/themes/woostore/functions/admin-init.php on line 69

Fatal error: require_once() [function.require]: Failed opening required ‘/home/barbara/public_html/wp-content/themes/woostore/functions/classes/class-wp-app-store-installer.php’ (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/barbara/public_html/wp-content/themes/woostore/functions/admin-init.php on line 69