Configuring your managed switch is kind of off topic for this forum, and configuring (or telling you how to configure, which is the same thing in the end) a used managed switch from afar, with no knowledge of how it was previously configured,
is really very difficult. Possibly your switch has been configured with multiple VLANs, or with some other unexpected (in a home) confguration which restricts traffic in some way.
HP acquired 3Com at some point; for documentation on 3Com switches before the aquisition you could look
here, and for products after you could look
here.
I'm not on the WHS team, I just post a lot. :)