求助：QT连接SQLserver的问题

代码如下：     QSqlDatabase dbconn=QSqlDatabase::addDatabase("QODBC");    QString dsn=QString("Driver={sql server};server=A43/DELL;database=Visitor;uid=aa;pwd=1234");    dbconn.setDatabaseName(dsn);    dbconn.setHostName(QString("127.0.0.1"));    dbconn.setPort(1433);    dbconn.setUserName(QString("aa"));    dbconn.setPassword(QString("1234"));    QTextCodec *BianMa=QTextCodec::codecForName("GBK");    bool r =dbconn.open();    if (r) {    qDebug() << "SQL Server 2000 Connect OK!";    QSqlQuery query = QSqlQuery(dbconn);    query.exec(BianMa->toUnicode("Insert into [tblTest] (F_cName,F_cSex) values('李四','女')"));    qDebug() << query.lastError().text();    qDebug() << dbconn.lastError();    } else {    qDebug() << dbconn.lastError().text();    } 错误："[Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server 不存在或访问被拒绝 [Microsoft][ODBC SQL Server Driver][DBNETLIB]ConnectionOpen (Connect()). QODBC3: Unable to connect"