Subdomain registration

Hi everyone, sorry for the trivial question but I am new here. I am trying to put a subdomain online with a different section of my site, but I do not seem to be able to. After I set it up (putting in the appropriate field), when I try to connect to it I get a “connection refused” error. Could it be because dreamhost does my hosting but I have not registered through them?
Also, I have now removed my subdomain configuration attempt from the “manage domains” window, but if I try to repeat the exact same process, I get an error saying “Can`t add domain, already in our DNS system”, even though I removed it!
It would be great if anyone could help
Thanks a lot