Hi,
So if I check your phpmyadmin, the highest value for the product_id in the hikashop_product table is 496:
monosnap.com/file/tLPKYKABpnS4PkOyuyW4vv2wXbzgO5
However, if I look at the information area of the table, I can see that the auto_increment value has been set to the value 4,294,967,296 which is invalid as it goes about the type (integer of 11 numbers) of the product_id column.
So I've updated your auto_increment value to 497. After that, everything worked again as it should:
monosnap.com/file/b8N3ytZ23f9klpDgkJANzbvqfpwr8W
So someone or something changed that value. If it's not you, it could some kind of database optimization extension or script gone awry.