I recently upgraded the hard drive on my Windows machine where I have Oracle 9.2.0 installed. I use this instance as a testbed for other applications that require database connectivity.
On my old hard drive, I had no issues, but now, when I attempt to connect to my test database, I receive an ORA-12505 error, indicating that the listener can't resolve my SID.
Since nothing had changed other than the physical hardware (the TNSNAMES.ORA and listener.ora files did not change) I am at a loss to understand what is going on. I did notice that in the Windows event viewer, the Oracle instance gets terminated, so I believe that there is something going on other than just the fact that I can't connect to the database.
If your Oracle instance is being terminated, there likely are other issues here. This would explain why you are receiving the TNS error when you attempt to connect -- the database is not available. What's not clear from your question is whether your instance is terminated prior to attempting to make a connection, or as a result of the connection attempt. Review the alert and listener logs for additional error messages. If the instance and database are crashing, there will hopefully be additional messages in the alert log to help diagnose what is happening. Another thing to check is the oradim log to see whether there are any errors reported there when your database opens (assuming that you have the service configured to automatically start your instance and open the database).
If you copied everything from your old disk to the new disk but did not re-install the Oracle software, you may also be encountering registry issues. Did the drive letter of your hard disk change (e.g., from C: to D:)? This would also create problems as there are paths stored in the registry related to Oracle.
This was first published in May 2006