OK.. I know questions about this particular error have been asked hundreds of times in this forum. I've read through the majority of them tonight and still can't seem to resolve my problem. Here's what is happening:
I'm running an Oracle 8.1.7 db on Windows 2000 server. Yesterday I change the sys and system password. Today I have to reboot the server because it had frozen. When I attempt to startup the db, I begin receiving listener errors. I decide to delete and recreate the service (my understanding is this also recreates the password file and should take care of any problems caused due to the password reset yesterday). I attempt to restart the db and receive the ORA-12560 error. I have checked and rechecked my tnsnames.ora and listener.ora files with no luck.
Sorry I didn't post a reply sooner. I have tried setting the oracle_sid before startup. I'm at the point now when I type connect internal and the pwd, I'm receiving login error ORA-00171: invalid username/password, logon denied.