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 (
1NULL '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 ...