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SQL SERVER:A network-related or instance-specific error occurred

I was using Microsoft SQL with asp.net MVC , it was working fine but today morning it gave me error :
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (.Net SqlClient Data Provider)
I tried to Enable TCP/IP. I also started SQL in configuration manager but still cannot login to SQL Server 2014 using cloud server. It was working fine. I don't know what has happened to it.
Thanks

There is a really good YouTube vid at the bottom of this web-page so you can rule out a few more things - failing that I would have the server rebooted.
SQL Authority

In MS SQL Server Management Studio, have you checked the Properties of the SQL Server to ensure that Allow remote connections to the server is ticked?
If so then I would have to agree that it an on the Cloud Server rather than an issue with the SQL database.
Are you able to reboot the Cloud Server?

MS SQL Studio 2014 doesn't work very well with SQL 2005 or older if you running an old database version

You may want to ensure that the cloud server is allowing connections from your remote IP. It could be that your remote IP address has changed and you are no longer allowed access.
How to open the SQL database firewall for Microsoft Azure:
https://azure.microsoft.com/en-us/documentation/articles/sql-database-configure-firewall-settings/

provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)

i am developing a web application in visual studio 2012. and i have added a database file named as Database1.mdf into App_Data folder and i have given following connection string
Data Source=(LocalDB)\v11.0;AttachDbFilename="E:\asp.net mvc\storage\storage\App_Data\Database1.mdf";Integrated Security=True
after that i have written the code for inserting the data but at that i am getting the error like
A network-related or instance-specific error occurred while
establishing a connection to SQL Server. The server was not found or
was not accessible. Verify that the instance name is correct and that
SQL Server is configured to allow remote connections. (provider: Named
Pipes Provider, error: 40 - Could not open a connection to SQL Server)
is there any mistake in the connection string?
Please help me in htis

Usually, for me, this indicates that SQL Server hasn't been configured correctly to receive remote calls. There are three things to check.
Your server instance is named correctly and you have permissions to it
That you are configured to receive remote connections
That SQL server is open on the the protocols you want to use
To check the second one, open up SQL Management Studio and select Properties on the server. Then check under "Connections" that "Remote Server Connections" is enabled.
To check the third, open up SQL Server Configuration Manager and make sure that "Client Protocols" TCP/IP is enabled as well as Named Pipes (depending on your network setup).

Your connection string should be written like this:
connectionString="DataSource=.\SQLEXPRESS; InitialCatalog=Database; AttachDBFilename=|DataDirectory|\Database.mdf; Integrated Security=SSPI;"

error in connect to sqlserver in windows and sql authentication mode

i have a snippet that it work properly when i use windowsmode with follow connection string
data source=.;database=xDB;integrated security=true;
but i have to change it for sql and windows mode i changeit to
Data Source=.;Initial Catalog=xDB;User Id=krs;Password=12345;
but follow error occur
Login failed for user 'krs'. The user is not associated with a trusted SQL Server connection.
and when change dot(.) to(local) another error occur
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
plz help me im beginer n confused.thank

You have to enable the Named Pipe & TCP/IP in SQL Server configuration. Go through following link to enable that
http://www.triostechs.com/Microsoft-SQL-Server-2008/Microsoft-SQL-Server-2008-Enable-TCP/IP-or-Named-Pipes.html
Also Make sure, only one instance of the SQL Server running. If it is more than one, just verify which one you are connecting to.

How to give database access to a program?

I created an MVC application that accesses my SQL Server database using LinqToSql. But I get an exception on dbGuestbookContext.SubmitChanges();
A network-related or instance-specific error occurred while
establishing a connection to SQL Server. The server was not found or
was not accessible. Verify that the instance name is correct and that
SQL Server is configured to allow remote connections. (provider: Named
Pipes Provider, error: 40 - Could not open a connection to SQL Server)
I can access other databases on that server from other applications.
Could you please tell what I can do about this?
Thaks.

ASP.NET Web application failed after bringing to test server

I am using VS2005 ASP.NET 2.0.
I have a web application which uses Active Directory Connection.
The application is able to run smoothly on my local machine, including logging in.
However, when I brought my web application to my test server, I am not able to log in and it gave me an error which says
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
What is happening? Is it because the AD I am connecting to does not allow remote connection? I am able to log in when I am on my local machine though.
EDIT:
I am able to connect to the SQL server.
I inserted the following code on my login page_load and there's no error
SqlConnection thisConnection = new SqlConnection("Data Source=<IP>;Initial Catalog=<database>;User ID=<username>;Password=<password>");
SqlCommand nonqueryCommand = thisConnection.CreateCommand();
thisConnection.Open();
thisConnection.Close();
Thus the error is most likely caused by the AD connection string. Looking for suggestions or solutions.

A database connection string you are using is either incorrect or the database you are attempting to connect to is not accessible.
If you are defining your connection strings in the web.config file, ensure these are relevant for the test environment you have deployed to.