Upgrade error is making me MAD !!!!

when trying to access wp-admin I get redirected to this address:
sitename.com/wp-admin/upgrade.php?_wp_http_referer=%2Fwp-admin%2F

Fatal error: Cannot redeclare get_temp_dir() (previously declared in /var/www/wordpress/wp-includes/functions.php:2168) in /var/www/wordpress/wp-admin/includes/file.php on line 189

I tried everything! uploading the wp-admin and wp-includes from the backup I had, I even tried uploading the new version’s folders, still the same.