You should have precise it in your first message.
So there is something missing in the check database for the restore of the root category in your specific case.
Please process that SQL query in your PHPMyAdmin (just replace the " #_ " with your database prefix).
Code:
INSERT IGNORE INTO `#__hikashop_category` (`category_id`, `category_parent_id`, `category_type`, `category_name`, `category_description`, `category_published`, `category_ordering`, `category_left`, `category_right`, `category_depth`, `category_namekey`) VALUES (1, 0, 'root', 'ROOT', '', 0, 0, 1, 22, 0, 'root'),(2, 1, 'product', 'product category', '', 1, 1, 2, 3, 1, 'product'),(3, 1, 'tax', 'taxation category', '', 1, 2, 4, 7, 1, 'tax');
Afterwards you might need to perform a "rebuild tree" via the HikaShop category listing toolbar.
But if you have purge your hikashop_category table ; I'm afraid that you might have other side effects.
