This problem will only plague Windows NT users. If you forgot to run ORADIM, or if you did not remember to issue a
SET ORACLE_SID=COIN command,
you may receive a TNS protocol adapter error when you start Server Manager. It will look like this:
Oracle Server Manager Release 18.104.22.168.0 - Production
(c) Copyright 1997, Oracle Corporation.
ORA-12560: TNS:protocol adapter error
You may also receive an unexpected password prompt. Either way, check to be sure that you have correctly set the ORACLE_SID environment variable, and then check the Services control panel to be sure that a service named OracleServiceCOIN exists. If it doesn't, you should back up one lesson and run the ORADIM command to create it.