WordPress upgrade unsuccessful

Fatal error: Call to undefined function update_core() in /home/dlsbins/public_html/wp-admin/includes/class-wp-upgrader.php on line 919

Trying to upgrade to 3.3.1

I had installed the plugin called WP-DBManager. It advised me to move the .htaccess file to the db-backup folder. I did and the only page that showed was the home page, all the links were broken.

.htaccess was restored, all pages were showing, THEN I tried to upgrade and the whole site is gone with only the fatal error message.

I am about to jump off a bridge, please help me.