dbconsole not starting

There can be many reasons why dbconsole might not start.
I am quoting one reason below.
Checke the logfiles at $ORACLE_HOME/hostname_sid/sysman/log
check the latest logs by doing a ls -ltr
In the file emagent.nohup
if you see something like this -
----- Thu Feb 11 14:05:44 2010::The agentTZRegion value in /home/oracle/oracle/product/10.2.3/av_1/sec_serverav/sysman/config/emd.properties is not in agreement with what agent thinks it should be.Please verify your environment to make sure that TZ setting has not changed since the last start of the agent.If you modified the timezone setting in the environment, please stop the agent and exectute 'emctl resetTZ agent' and also execute the script 'mgmt_target.set_agent_tzrgn' to get the value propagated to repository -----
....then give the follwoing command
emctl resetTZ agent
then login as sysman/password and run the following command-
SQL> exec mgmt_target.set_agent_tzrgn('sec:3938','Asia/Calcutta')
PL/SQL procedure successfully completed.