oracle crash - not starting
Be sure the ORACLE_HOME and ORACLE_SID environment variables are correctly set. Then run sqlplus / AS SYSDBA as a user who is a member of the oradba group on the computer.

Get the machine down forcibly:

SHUTDOWN ABORT


Start it up, but try not to let stuff run wild:

STARTUP RESTRICT


Shut it down more gracefully. Don't stop until recovery is complete.

SHUTDOWN IMMEDIATE


Start it up.

STARTUP