连接sql server 2000 报错

com.microsoft.sqlserver.jdbc.SQLServerException: 通过端口 1433 连接到主机 localhost 的 TCP/IP 连接失败。错误:“Connection refused: connect。请验证连接属性，并检查 SQL Server 的实例正在主机上运行，且在此端口接受 TCP/IP 连接，还要确保防火墙没有阻止到此端口的 TCP 连接。”。
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(SQLServerException.java:171)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(SQLServerConnection.java:1033)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:817)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:700)
at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:842)
at java.sql.DriverManager.getConnection(DriverManager.java:525)
at java.sql.DriverManager.getConnection(DriverManager.java:140)
at org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:110)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:423)
at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144)
at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:119)
at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:57)
啥原因？