The instance name must be the same as computer name.

when you changed the Computer Name when there is already a SQL Server 2005 instance running (exists) in your system, then you may have to face “The instance name must be the same as computer name” at the time of installing the Microsoft CRM 4.0 Server.

As the solution you have to make sure the exact name of the SQL Server instance running in your computer. for that execute the following command in Query Analyzer :

select @@Servername

if the above commands gives you the output as the old server name

Then execute the following command:

sp_dropserver 'old_sql_server_instance_name', 'droplogins'
GO
sp_addserver 'new_sql_server_instance_name', 'local'
GO