1. Fire up your SQL *PLUS and log in with SYSDBA priveledges.
START > RUN > sqlplus
SQL > CONNECT sys/passTheAdmin AS SYSDBA
2. Issue a Shutdown command
SQL > SHUTDOWN IMMEDIATE;
3. Mount yourDatabase
SQL > STARTUP MOUNT;
4. Set your database in ARCHIVELOG mode
SQL > ALTER DATABASE ARCHIVELOG;
5. Open your database
SQL > ALTER DATABASE OPEN;