I got this error after working at distance (VPN) for a few years. At some point in time I must have changed my DNS settings to the IP address of my home router. Now I was (again) in the same network as the server, and got the error above. the solution was to open "Network status" / "Change adapter options" and right click the active internet connection (Ethernet in my case) to get to the properties of IPv4. Under "Use the following DNS server addresses" I entered the local IP address of my server, and what do you know...! The computer contacted the domain (on the server) and SQL Server opened up.

要检查是否有相同的问题，打开cmd并输入 夜间电报/ dsgetdc:域名 [用域名交换"domainname"] 如果您得到一条消息说“获取DC名称失败:Status = 1355 0x54b ERROR_NO_SUCH_DOMAIN”，您可能是域名错误，或者您可能有这个问题。

在做了上面提到的所有事情之后: http://blog.sqlauthority.com/2009/05/21/sql-server-fix-error-provider-named-pipes-provider-error-40-could-not-open-a-connection-to-sql-server-microsoft-sql-server-error/ 对我来说还是没用。

以下步骤对我很有效:

开始>执行> cmd > sqlcmd -L

它将提示您服务器名。确保此服务器名称与SQL management studio的CONNECT to server框中试图连接的服务器名称相同。

我犯了这个愚蠢的错误，我一直使用MSSQLSERVER而不是使用这个服务器名。

希望这对像我一样犯愚蠢错误的人有所帮助。

谢谢。

这也可能是简单的事实，你的数据库实际上不是MS SQL Server。例如，如果你的数据库实际上是MySql，你试图用System.Data.SqlClient连接它，你会得到这个错误。

到目前为止，大多数ADO的例子。Net将用于MSSQL，没有经验的用户可能不知道你不能在MySql中使用SqlConnection, SqlCommand等。

虽然所有的ADO。Net数据提供程序遵循相同的接口，您必须使用为您的数据库提供程序。

I had the same issue after upgrading my Windows to Windows Pro 10 21H2. I have two SQL instances - 2014 and 2019 and I was not able to connect only to 2019 one. I restarted the computer, restarted all SQL related services. Two of the services were showing errors (SQL Server and SQL Server agent) and I was not able to start them. I could not also start these two services from C:\Windows\SysWOW64\SQLServerManager15.msc In the logs (C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER01\MSSQL\Log) I saw these lines:

Initializing the FallBack certificate failed with error code: 15, state: 29, error number: 0.
Error: 17190, Severity: 16, State: 1.
Unable to initialize SSL encryption because a valid certificate could not be found, and it is not possible to create a self-signed certificate.
Error: 17182, Severity: 16, State: 1.
TDSSNIClient initialization failed with error 0x80092004, status code 0x80. Reason: Unable to initialize SSL support. Cannot find object or property. 
Error: 17182, Severity: 16, State: 1.
TDSSNIClient initialization failed with error 0x80092004, status code 0x1. Reason: Initialization failed with an infrastructure error. Check for previous errors. Cannot find object or property. 
Error: 17826, Severity: 18, State: 3.
Could not start the network library because of an internal error in the network library. To determine the cause, review the errors immediately preceding this one in the error log.
Error: 17120, Severity: 16, State: 1.
SQL Server could not spawn FRunCommunicationsManager thread. Check the SQL Server error log and the operating system error log for information about possible related problems.

原来在升级后，服务的“Log On”属性(服务属性上的第二个选项卡)被设置为NT AUTHORITY\NETWORK SERVICES。当我将其更改为“本地系统帐户”时，我能够启动服务并连接到MS SQL 2019实例。

这个msdn论坛的帖子帮助我找到了这个。

我使用的是SQL Server 2016和windows 10。

首先是允许远程连接到SQL Server。 我所做的就是键入sqlservermanager13。在开始菜单打开SQL Server配置管理器。确保TCP/IP状态为启用状态。

双击TCP/IP协议名称，检查TCP端口号。通常默认值是1433。

以下步骤通过使用Microsoft管理控制台(MMC)管理单元配置Windows防火墙的高级安全。高级安全Windows防火墙只配置当前配置文件。

To open a port in the Windows firewall for TCP access On the Start menu, click Run, type WF.msc, and then click OK. In the Windows Firewall with Advanced Security, in the left pane, right-click Inbound Rules, and then click New Rule in the action pane. In the Rule Type dialog box, select Port, and then click Next. In the Protocol and Ports dialog box, select TCP. Select Specific local ports, and then type the port number of the instance of the Database Engine, such as 1433 for the default instance. Click Next. In the Action dialog box, select Allow the connection, and then click Next. In the Profile dialog box, select any profiles that describe the computer connection environment when you want to connect to the Database Engine, and then click Next. In the Name dialog box, type a name and description for this rule, and then click Finish.

另一个需要配置的东西。

To open access to SQL Server when using dynamic ports On the Start menu, click Run, type WF.msc, and then click OK. In the Windows Firewall with Advanced Security, in the left pane, right-click Inbound Rules, and then click New Rule in the action pane. In the Rule Type dialog box, select Program, and then click Next. In the Program dialog box, select This program path. Click Browse, and navigate to the instance of SQL Server that you want to access through the firewall, and then click Open. By default, SQL Server is at C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Binn\Sqlservr.exe. Click Next. In the Action dialog box, select Allow the connection, and then click Next. In the Profile dialog box, select any profiles that describe the computer connection environment when you want to connect to the Database Engine, and then click Next. In the Name dialog box, type a name and description for this rule, and then click Finish.

看看微软的文档 配置Windows防火墙访问数据库引擎

我也遇到过同样的问题 就我而言，我用这种方法解决了问题

步骤1:从开始菜单进入SQL server配置管理器

步骤2:启用TCP/IP

步骤3:双击TCP/IP，进入IP地址最后一个条目IP ALL，输入TCP端口1433然后应用

第四步:然后按win+r，写服务。msc打开服务，然后向下滚动，然后右键单击SQL Server (MSSQLSERVER)选择重新启动

这解决了我的问题。 即使做以上所有步骤都不能解决问题，然后简单地重新启动PC，希望它会工作。