Enterprise Manager

After logging into the OEM as a SYS user , I was able to mount the database . The Database status shown to me as below,

Listener - up
Agent Connection to the Instance - unavailable
Database instance- down - message - Enterprise Manager is not able to connect to the database instance.

After that I tried to connect to the database through sql developer , I was able to connect using connection for the SYS user and able to run the queries .d

So How can I be able to connect to the Database Instance using OEM ?

Please suggest me what to do or what to check ...

Your help will be appreciated...