You could manually add a category, category_description and change the products_to_categories table from categories_id 0 to match the value you manually added via phpMyAdmin ...
Backup your database before attempting this ...
PHP Code:
INSERT INTO `categories` ( `categories_id` , `categories_image` , `parent_id` , `sort_order` , `date_added` , `last_modified` , `categories_status` )
VALUES (
1, NULL , '0', NULL , NULL , NULL , '1'
);
INSERT INTO `categories_description` ( `categories_id` , `language_id` , `categories_name` , `categories_description` )
VALUES (
'1', '1', 'TEMPORARY', ''
);
UPDATE products_to_categories set categories_id=1;
Then go to the Tools ... Store Manager ... and run the Update Master Categories ID ...
Then run the Update Products Price Sorter ...