IMPORTANT: Do not change the database settings until you are sure of what you're doing.
This error is usually caused by the ConQuest database that cannot be reached if you are on a Network install and or someone had run the latest ConQuest Update. The first things to check are:
If there have been no updates, it will likely be an issue with the connection/server running the SQL Database. You can confirm this by asking if anyone else can connect to the database.
If you know which machine has the ConQuest database on, ensure that it is on and responding. The SQL (CONQUEST (Instance name)) Service on the machine running the Database should be running.
Note: The SQL database is not necessarily on a server - Microsoft recommends not putting SQL Server on a domain controller, so if you only have one server, the SQL is likely elsewhere. If you don't know where it is, ConQuest support should be able to tell you.