You have to enable TCP/IP connections to access the database through navicat.
Open SQL server configuration manager and:
Turn on TCP\IP port (SQL Server Network configuration = > Protocols for <your database name>)
Fill up that form like this:
(replace IP to yours, TCP IP port is 1433 and use dynamic ports value is 0)
You can access HappyTool from other computer than localhost without any necessary configurations. Of course you must have a happy tool manager account.