The scenario is the following one:

An internal server physical where is installed SQL Server 2014 (Windows Server 2012 R2), a virtual server (DMZ) where is located the site, DNN, IIS and a SQL management studio to test connectivity to the server.

1 week ago DB server crashed so we had to reinstall it, SQL is already installed and working (another internal Apps are running well). Site DB have been restored from SQL and user assigned to that site has public and dbowner grants assigned, connection from DMZ to database is tested using sa and website user via SQL Management Studio but this error appears: "DNN Error Connection to the database failed (Return to Site)"

Any ideas please. This is my public website and noone can access.