How to Drop Dbconsole and repository – Enterprice Manager in 10g
emca -deconfig dbcontrol db -repos drop

Enter the following information:
Database SID: AARTHI
Listener port number: 1521
Password for SYS user:
Password for SYS user: password
Do you wish to continue? [yes(Y)/no(N)]: Y
Apr 11, 2010 7:47:37 AM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at C:\oracle\product\10.2.0\db_1\cfgtoollog
s\emca\aarthi\emca_2010-04-11_07-47-10-AM.log.
Apr 11, 2010 7:47:41 AM oracle.sysman.emcp.EMDBPreConfig performDeconfiguration
WARNING: EM is not configured for this database. No EM-specific actions can be p
erformed.
Apr 11, 2010 7:47:42 AM oracle.sysman.emcp.EMReposConfig dropRepository
INFO: Dropping the EM repository (this may take a while) …
Apr 11, 2010 7:48:07 AM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully dropped
Enterprise Manager configuration completed successfully
FINISHED EMCA at Apr 11, 2010 7:48:07 AM

How to Create Dbconsole – Enterprice Manager in 10g

emca -config dbcontrol db -repos create
C:\Documents and Settings\user1>emca -config dbcontrol db -repos create

STARTED EMCA at Apr 11, 2010 7:52:24 AM
EM Configuration Assistant, Version 10.2.0.1.0 Production
Copyright (c) 2003, 2005, Oracle. All rights reserved.

Enter the following information:
Database SID: AARTHI
Listener port number: 1521
Password for SYS user:
Password for DBSNMP user:
Password for SYSMAN user:
Email address for notifications (optional): aarthimudhalvan@gmail.com
Outgoing Mail (SMTP) server for notifications (optional): smtp.gmail.com
—————————————————————–

You have specified the following settings

Database ORACLE_HOME ……………. C:\oracle\product\10.2.0\db_1

Database hostname ……………. lokesh.fletsphone
Listener port number ……………. 1521
Database SID ……………. AARTHI
Email address for notifications …………… aarthimudhalvan@gmail.com
Outgoing Mail (SMTP) server for notifications …………… smtp.gmail.com

—————————————————————–
Do you wish to continue? [yes(Y)/no(N)]: Y
Apr 11, 2010 7:53:44 AM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at C:\oracle\product\10.2.0\db_1\cfgtoollo
s\emca\aarthi\emca_2010-04-11_07-52-24-AM.log.
Apr 11, 2010 7:53:57 AM oracle.sysman.emcp.EMReposConfig createRepository
INFO: Creating the EM repository (this may take a while) …

How to recreate Dbconsole repository – Enterprice Manager in 10g
emca -config dbcontrol db -repos recreate