While installing the database some time due some problem, everything is installed but enterprise manager does not work.

In another common case (I am not really talking about production servers here) due to some reason like change in ip addresses and so on, enterprise manager stops working.

Whatever the case, In simple words there is a requirement that we need to drop the existing setup of enterprise manager and create new one with new configuration.

Note here I am only talking about dropping and then creating again which I normally do with my development server off course there are other options too.

First drop the present configuration and its repository as follows:

C:\>emca -deconfig dbcontrol db -repos drop

It will ask for following related to your database:
Database SID: dcs
Listener port number: 1521
Password for SYS user:******
Password for SYSMAN user:*****

After entering above information just follow the instruction on the screen.

Then create the new configuration and its repository as follows:

C:\>emca -config dbcontrol db -repos create

It will ask for following related to your database:
Database SID: dcs
Listener port number: 1521
Password for SYS user:******
Password for DBSNMP user:******
Password for SYSMAN user:******
Password for SYSMAN user: Email address for notifications (optional):
Outgoing Mail (SMTP) server for notifications (optional):

After entering above information just follow the instruction on the screen.

Thats it!