Oracle complains again - Shutting down or initialisation in progress

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.

Oracle OEM wrong password

Problem:
Although you are damn sure the password is right, but OEM simply doesn't agree.

Solution:
You might have changed your security policies (hardened??).
GO local security policy, add the windows/AD user to 'Log on as batch job'

Oracle OEM died

Problem:
I only changed my Oracle server's IP or hostname and the whole Oracle Enterprise Manager thing died on me!

Solution:
Oracle OEM depends on the IP and Hostname that is during the installation. So if its changed, things will go wrong.

Soln:

Perform the following steps.
1) Run the following, this will remove entire OEM setup from Oracle
emca -deconfig dbcontrol db -repos drop

2) RUn the following, this will remove the orphaned OEM console service
sc delete consoleServiceName

3) Remove the existing listener with Net Configuration Assistant.

4) Change listener.ora and tnsnames.ora to fit the current IP and hostname settings.

5) Restart the remaining oracle services. (Restart comp if not sure)

6) Add new listeneer with Net Config Assistant

7) Ensure Listener and Database instance are up
Run the following, this will reinstall the entire OEM setup for oracle.
emca -config dbcontrol db -repos create


8) Open the Enterprise Manager Console and try again

Oracle database cannot start

Problem:
Oracle database 10g simply refuse to start.

Possible solutions:
1) The listener may not be working properly. If sample database was not created during first database creation, then a listener is not included in installation. Run Net Configuration Manager to create a new listener.

2) System just rebooted, services has not started yet. Type services.msc and check if the oracle services are up.

Oracle cannot connect

Problem:
'Cannot connect to database using existing credentials".
This may happen even though you are damn sure you got the username and password correct.

Possible Solution:
Oracle do not accept certain characters such as '.' and ';' and probably many others. So to be safe, use alphanumeric characters.
* During the setting of username and password, Oracle won't complain of illegal characters, but when it comes to logging in, the above error occurs *