Adding a data file

I need to add a data file, but my user account doesn't have privileges. I have connected to the oracle as sqlplus / as sysdba and it is telling me I'm connect to an idle instance. How can I connect to my database and create a data file if I don't know the passwords of any of the account that have privileges to do so?

Background: I inherited this database from an admin that has left and didn't leave any passwords.

Thank you for any information you can provide.

Hi,

If you get connect runing "sqlplus / as sysdba" so you are connected with dba role, you can add data file.
the message "connect to an idle instance" is because you instance is down, run startup to start the instance.
If a datafile is missing or been corrupted the instance will show a message, restore datafile from your backup and apply archived logs, if necessary.

Quim&r@