Follow these rules for changing Oracle Database system privileges account passwords.
Before you use a locked account, you must unlock it and reset its password. Passwords for all Oracle system administration accounts except SYS, SYSTEM, and DBSNMP are revoked after installation. If you created a starter database during the installation, Oracle Database Configuration Assistant displays a screen with your database information and the Password Management button. Use the Password Management button to unlock only the user names you use.
For more information about how to create a secure password, see: