OEM Agent is showing "Down" status
This indicates the status of the connection between Oracle Enterprise Manager (OEM) and the database under investigation.
Since OEM is web based , it will show Down if it looses its connection.
You might want make sure that you are able to connect with your OEM to this same database that shows status "down".
Also, when you right click on that word Down, the drop down menu will show if the status if getting refreshed or not, please make sure it is refreshed.