Fail to start Oracle Enterprise Manager 11g

I will post how to recover Oracle Enterprise Manager (OEM) for 11g when failing to start OEM after changing the password of sysdba. Normally OEM is working well. However, OEM has a problem after changing the password sometimes. To fix this problem, you can reconfigure the setting of OEM.
Here is a way.
First of all, type the following command.

oracle> emca -deconfig dbcontrol db
oracle> emctl start dbconsole
   -> after doing this command, if OEM is not working, try to run this command.
oracle> emca -config dbcontrol db

Enter the following information:
Database SID: bm
Listener port number: 1521
Listener ORACLE_HOME [ /db/app/oracle/product/11.2.0/dbhome_1 ]:
Password for SYS user:
Password for DBSNMP user:
Password for SYSMAN user:

Enter your database SID, listener port, oracle home, and the passwords of SYS, DBSNMP, SYSMAN.

This command will reconfigure all the settings for OEM.