Please make sure the required service pack and database settings are installed and configured properly.
From our experiences, the user also failed to configure the following items:
1. The users do not install corresponding correct SQL Service Pack. Ensure that SQL Server 2000 is installed together with SP4, and SQL Server 2005 is installed together with SP1.
2. During installation in Express 2005, we should select default instance MSSQLSERVER NOT SQLEXPRESS instance.
Now should check from the Service: the MSSQLSERVER instance should be running, if not, please re-install again as you selected the instance wrongly during setup.
3. After the server was installed, the users forgot to check and configure the server settings in SQL Server Configuration Management e.g. enable the required protocol Named Pipes AND the log on must be “LocalSystem”.
Most of the users can solve those problems after the above checking.