If you change the name of a computer running SQL server you must also update the system metadata stored in sys.servers.
First check the current name by using
If @@SERVERNAME does not show the correct computer name you should change it using the following commands:
sp_addserver <new_name\instancename>, local
Last step is to restart the SQL Server instance.
How to: Rename a Computer that Hosts a Stand-Alone Instance of SQL Server