We faced this issue on one of our servers which was due for a restart.
Many blogs suggested that the Named Pipes be enabled, and that the order of the named Pipes vis-a-vis TCP/Ip be changed.
When i checked the errorlog, it showed :
SQL Server is terminating because of a system shutdown. This is an informational message only. No user action is required.
Service Broker manager has shut down.
SQL Trace was stopped due to server shutdown. Trace ID = ‘1’. This is an informational message only; no user action is required.
The SQL Server Network Interface library could not deregister the Service Principal Name (SPN) for the SQL Server service. Error: 0x45b, state: 4. Administrator should deregister this SPN manually to avoid client authentication errors.
Some more Googling led to a possible issue with an incorrect shutdown of the services. The “SPN” is related to Active Directory, and in some cases with Kerberos.
The server was restarted and the issue was solved in this case. Note: the other methods like Named Pipes enabling did not help here.
Some useful references :