can't say for sure but it sounds like you're doing everything right MIDI connections/ settings wise. THe only thing that you could check (and I don't know whether or not this even applies to Clavia synths) if your Nord is set to a single or multi mode. If it's set to a multi mode and it just happens to be an empty multi then obviously you won't get any sound. Also, MIDi assignments within the multi itself could play an important role. For example the multi program change receive channel is set to 1 but the actual parts are set to channels 5 through 9 or something. Just giving you an example here.
Could also be anything as simple as a bad MIDi cable or main out volume being muted/ turned down all the way. Don't forget the simple things. It's often the simple stuff that gets overlooked.
If you have no luck finding answers here then try
www.virusti.com and may be Clavia Yahhoo user groups. I'm sure it's something simple though and you'll figure it out sooner or later.
cheers,