Can you try to add the System again in ePO?
GO to System tree, System actions -> new System ->and you can add it by IP or hostname.
Maybe it's an EEPC standalone installation (if it's an old EEPC version). The best way to check if it's managed by ePO or not (even if it doesn't appear under system tree) is to open a web browser on the computer itself and go to http://localhost:8081 and check at the top of the page if there's an ePO server there
You can remove eepc with eetech if you know the user name and password.
What version of eepc do you have?