When I am using an actual MS SQL Server install such as SQL Express (not the database file that accompanies DNN) my connection string looks more like:

add name="SiteSqlServer"connectionString="Server=(local);Database=DNNDB;uid=dnn_user;pwd=dnn_user;"providerName="System.Data.SqlClient"

Since you are using a named instance, replace Server=(local) with Server=LOUIS-MOBILE\MSSMLBIZ 

If you don't already have a working install of DNN on that SQL Server, first create a new database (I called it DNNDB in the connectionstring above; call it what you want). Then create a login on the server called "dnn_user" or whatever you want to call it. Then make sure you are in the db you just created and run

EXEC sp_changedbowner 'dnn_user'

Do NOT make the login a user on that database before running that sproc - just create the login. When you run that sproc it will make that login the default dbo user on that database.

Then make sure your connection strings aim at that server, at that database, with that userid and its password ... you should be good.