SQL Server 2005 login error

SQL Server 2005: While login Error 18452 (not associated with a trusted sql server connection)

I found the following simple solution

Go to Start > Programs > Microsoft SQL Server 2005 > 
SQL Server Management Studio
Right-click the Server name, 
select Properties > Security
Under Server Authentication, 
select SQL Server and Windows Authentication Mode
The server must be stopped and re-started before this will take effect..."

It has solved my problem, so I hope it could be helpful for you too.