当sql server实例停止时发生此错误。

进入所有程序>SQL Server >配置工具>SQL Server配置管理器

然后点击SQL sERVER SERVICES，实例列表将出现，选择实例问题，并点击顶部工具栏上的播放图标，希望这将有所帮助。

这个答案很晚(但晚总比不到好;)

我通过打开服务来解决这个问题，然后开始运行Sql Server (Sqlexpress)服务。

当我在Visual Studio中遇到这个错误时，

"在建立与SQL Server的连接时，发生了与网络相关或特定于实例的错误。未找到服务器或无法访问服务器。验证实例名称是否正确，SQL Server是否配置为允许远程连接。(提供商:命名管道提供商，错误:40 -无法打开到SQL Server的连接)"

.．.它是在执行下面的c#代码期间，它试图获取我的SQL Server数据以在网格中显示。中断恰好发生在表示connect.Open()的行上:

        using (var connect = Connections.mySqlConnection)
        {
            const string query = "SELECT Name, Birthdate, Narrative FROM Friends";
            using (var command = new SqlCommand(query, connect))
            {
                connect.Open();
                using (var dr = command.ExecuteReader())
                {
                    while (dr.Read())
                    {
                        // blah
                    }
                }
            }
        }

It was inexplicable because the SQL query was very simple, I had the right connection string, and the database server was available. I decided to run the actual SQL query manually myself in SQL Management Studio and it ran just fine and yielded several records. But one thing stood out in the query results: there was some improperly encoded HTML text inside a varchar(max) type field within the Friends table (specifically, some encoded comment symbols of the sort <!-- lodged within the "Narrative" column's data). The suspect data row looked like this:

Name    Birthdate    Narrative
====    =========    ============== 
Fred    21-Oct-79    <!--HTML Comment -->Once upon a time...

注意编码的HTML符号“&lt;”，它代表一个“<”字符。不知何故，它进入了数据库，而我的c#代码无法接收它!它每次都失败在connect.Open()行!在我手动编辑数据库表Friends中的一行数据并输入解码后的“<”字符之后，一切都正常了!这一行应该是这样的:

Name    Birthdate    Narrative
====    =========    ============== 
Fred    21-Oct-79    <!--HTML Comment -->Once upon a time...

我使用下面这个简单的UPDATE语句编辑了一个不好的行。但如果你有几行违规的HTML编码，你可能需要一个更详细的UPDATE语句，使用REPLACE函数:

UPDATE Friends SET Narrative = '<!--HTML Comment -->Once upon a time...' WHERE Narrative LIKE '&lt%'

因此，这个故事的寓意是(至少在我的情况下)，在将HTML内容存储到数据库之前清理它，这样您就不会在第一时间得到这个神秘的SQL Server错误!(如果你需要更多信息，正确地消毒/解码你的HTML内容是另一个值得单独在StackOverflow搜索的讨论主题!)

我将使用Entity Framework的项目设置为启动项目，然后运行update-database命令，解决了这个问题。

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。

按window + R(运行窗口打开)，在运行窗口类型“服务”。msc”和新服务打开找到实例名SQL SERVER在我的情况下，它是SQL SERVER(SQLEXPRESS)，然后启动这个服务，再试一次，它为我工作，希望它也为你工作。