On SQL Server 2005 Express Edition (I don’t know how’s on full version, never had a license for it) the default connection model is through named pipes and TCP/IP is disabled.
If you want to connect to it from Oracle SQL Developer using jTDS driver it will throw a generic connection failure, as he is trying just TCP/IP. The error looks like this:
1. From SQL Server Configuration Manager, go and expand “Network Configuration”, choose “Protocols for SQL Server Express” and enable TCP/IP
2. Open TCP/IP properties page, go to the second tab “IP Addresses” and in the last field called “IPAll – TCP Port” enter your port number. You might want to choose 1433.
3. Restart SQL Server Express service.
4. JDNI Connection Sample: