If you make changes to the SQL Server Registry entries, then you should first back up those entries by using the Regrebld -backup command-line utility. Usage is:
You can run this command from the Command Prompt. Regrebld with the backup parameter creates five files in the Mssql7Binn folder: mssql7.rbk, mssql7ct.rbk, mssql7ea.rbk, mssql7es.rbk, and mssql7p.rbk. After editing the Registry, if you encounter any problems, than you can restore the SQL Server Registry entries by running Regrebld with the restore parameter. Usage is:
If you run the Regrebld utility without any parameters, it restores the registry entries, as with the -Restore option and re-creates the SQL Server services.