I installed oracle 8i on my PC . But when I started sql plus
With following login

User id: system
Password: manager

Following error was displayed:
TNS protocol adapter error 12560

And I could not log connect to oracle
Listener service is running at startup
I restarted the service but problem was not resolved

What is the solution
Please tell

Your TNS names file (TNSNAMES.ORA) has to be pointing to your Oracle instances. Each instance has a name and will be listening on a port. Example:

INSTANCE1 = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = server_name)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = service_name )))

INSTANCE2 = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = server_name)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = service_name )))

To test connectivity, go to a command prompt and type TNSPING80 instance_name.

You should get a reply with an OK.