How to Recover My Oracle 9i Database From Just The Datafiles The state of the system when I started was that there was a single, working instance of Oracle Database 9i. I proceeded to install Oracle 11g choosing to Install Software Only. Upon completion, everything still worked fine. I created a new 11g listener on port 1522 called LISTENER, which was the same name as the 9i listener listening on port 1521. I don't know if things still worked at this point. Next, I started creating an 11g database which I gave the same SID as the pre-existing 9i database. The database creation process failed at first, and I didn't read the error messages. I ran it again, and no error messages came up. It was at this point when people started complaining about being kicked out of the database.

Upon investigation, I found that it was completely impossible to connect to the once flawless db instance. I tried a myriad of things to get connected to no avail. Finally, I decided I would be better off creating a separate instance and accessing the datafiles from there. This is what brings me here. I have tried creating an instance with the same datafile names and copying the originals into the directory, but I don't know what the original configuration is so that inevitably failed. If anyone has any advice on how I can gain access to the datafiles without knowing the original configuration, I would greatly appreciate it.

OS: Windows Server 2003 R2

Pastebin of 9i alert.log here.
Seeing as you have stated that the original data files look like they're untouched, all you need to do is recreate the service with oradim, making sure you're using the 9i ORACLE_HOME service and tools.