We have come across to the situation where we couldn't login to the grid.
However, after checking the certin components of the GRID server we come to the know that everything is running but some concerns have been taken place in my mind that, it would be better if we could check and view the registerd databases from repository.
Please let me know if we can check the registerd databases through sql prompt from the EM repo.
Please confirm the version of Grid Control.
Confirm if the "emctl start oms" works fine with out any issues.
Upload the output of the command "emctl status oms -details".
Based on the Grid Control version will provide you the test how to verify the connectivity. But if the repository connectivity is the problem, you will not even get the Console.
i would suggest to raise a Service Request with Grid Control team.