The user.config overrides what is in the web.config but the user.config isn't reloaded when it is changed. So, make sure the user.config connection string is correct and then touch the web.config.
If SQL Server is installed on the same machine as IIS running your website, your connection string should probably look like this:
<add key="MSSQLConnectionString" value="Server=.\;Database=mojoportal;User Id=mojouser;
Password=thepassword;"/>
If you are using a named instance of sql server on the same machine as IIS running your website, you connection would look like this:
<add key="MSSQLConnectionString" value="Server=.\NAMEOFINSTANCE;Database=mojoportal;User Id=mojouser;
Password=thepassword;"/>