a couple of things come to mind:
if you created a new user, the file space might well be empty except for invisible files (names the begin with a .) You may have to turn on something like "show invisible files" to be be able to see them. That may explain why it says connected but looks empty.
Navigate to manage domains in the panel, and find the domain in question. in the webhosting column it should say "fully hosted, user: " whatever user name is there is the user you need to use to log in.
If you think the problem is a bad password then go to "manage users" in the panel, edit the user to change the password. Wait 10 minutes or a little longer and you should be able to log in using the new password.