A lot of my customers told me that after upgrading their windows 7 / 8.1 machine they can't connect any more to sql server.

I replicated the problem here on a test machine and I have the same problem too.

Scenario:

Windows 8.1 + SQL Server 2014 Express.
On the server: I open Management Studio and try to connect to [ServerName]\[InstanceName]. It works.
On any client: I try to connect to [ServerName]\[InstanceName] (with a .NET application) and it works.

I do the upgrade to windows 10 on the server. After the upgrade:

On any client: I try to connect to [ServerName]\[InstanceName] and it works
On the server:

• I open Management Studio and try to connect to [ServerName]\[InstanceName] (same operation as above). It doesn't work (timeout: cannot find the server/instance specified).
• I open a .NET application and try to connect to [ServerName]\[InstanceName]. It doesn't work (timeout: cannot find the server/instance specified).
• I open a command prompt and I type OSQL -S [ServerName]\[InstanceName] -E and IT WORKS.
• I open Management Studio (or any .NET app) and try to connect to [ServerIP(V4)]\[InstanceName]. IT WORKS.
  

I tried to "repair" the sql server installation but it stops at the "SqlEngineDBStartConfigAction_repair_configrc_Cpu64" (I suppose it tries to connect to the just restored sql server instance to configure it) pic below:

Is there any official fix or KB article on how to fix this?

Thank you.

• Edited by LinoB 22 hours 25 minutes ago

Can you check SQl Server is up and running. Have you verified it. Can you go to SSCM and check the status of the services

Did you having the same language for Windows 10 and SQL Server ?

Was this SQL Server an upgrade ?

http://connectbeta.microsoft.com/SQLServer/feedbackdetail/view/974626/cannot-uninstall-sql-express-2014-on-windows-7-sp1

https://social.msdn.microsoft.com/Forums/en-US/70436563-31ee-40bb-9324-3f6a03e5bd3f/sql-server-express-2014-on-windows-10?forum=sqlexpress

Of course it is or clients couldn't connect either.

Services:

Sql Server: Running/Automatic/"LocalSystem"
Sql Server Agent: Stopped/Other(Boot, System, Disabled or unknown)/"NT AUTHORITY\NETWORKSERVICE"
Sql Server Browser: Running/Automatic/"NT AUTHORITY\LOCALSERVICE"

Yes. Same language.

Windows 7 italian. -> Windows 10 Italian.

SQL server Express 2014 Italian.
SQL Server installed from scratch.

By trial and error I found where the problem actually is.

It seems that disabling SHARED MEMORY (in sql server protocols) causes the problem after upgrading to Windows 10.
Let me explain. On some windows 7 systems, with Shared memory enabled, the server couldn't connect to itself (don't ask me why).

Our setup procedure disabled shared memory protocol immediately after install leaving the server as:

1. Shared memory (disabled)
2. Named pipes (enabled)
3. TCP/IP (enabled)

Client protocols, instead, were left as default (all enabled in this order SM/NP/TCP)

SQL Server on Windows 7 or Windows 8/8.1, with that configuration, works without problems. After the OS upgrade, with that configuration, you can't connect from the server to the server itself any more. Not even uninstalling and reinstalling SQL Server from scratch.

Could any of you please confirm that disabling Shared memory on Win10 prevents the connection to you too?
Can you reproduce it too?

• Marked as answer by LinoB 7 minutes ago