Have you tried selecting your driver and entering the user, password, etc.?
If that does not work, what is the error message?
Only then should you look at using custom connection strings.
If you need to use a custom connection string, you should use the format that is in your documentation for the driver that you wish to use. If you cannot find it there, then you can have a look here: http://www.connectionstrings.com/
But please try connecting without using a custom connection string first.