Have you seen a log file ??? What does the event viewer tell you???
Is it a problem with not having the management server configured
with sysman (remember upon the installation of the console, the password must be changed.
Is it Client that u installed.
If it is the server ,no need of NT card,else u should need NT card to connect to the Database.
Again is the Managment server repository database on the same m/c.If not again u need the NT card.
Check whether there is a OEM_REPOSITORY tablespace in the database.
Check the Oracle Management service whether is it started.
Check to start OEM in standalone mode.
If nothing works,take the Management server Config tool create a new management server and try.