Problem:
Sometimes Oracle simply flashes the following message or something similar.
Shutting down or initialization in progress.
There's nothing you could do, even after u waited for ages for it to complete its cycle.
Solution:
This is unorthodox, but me being bad programmer, i choose to solve the problem first before looking for detailed explanations.
Log in under SQLPlus with following command.
sqlplus sys/yourpassword as sysdba
Then run the following SQLPLUS commands.
shutdown immediate;
startup;
Sometimes of order of the SQLPlus command needs to be reverse, depending on its state.