Well all I can help with is thoughts on the basics. Have you checked you various volume levels in the Control Panel -> Multimedia -> Properties kind of places? Make sure your line-in volumes are not
muted. Also, as you produce sound try and get behind the computer and check the cable in the line-in.
Make sure it is engaged properly. I actually had one cable I used that, if pushed it all the way in gave
me only one channell. I had to actually pull it slightly out to get two channells. I probably had the
wrong cable connector type.

Try attaching a different type of component to that jac. See if anything
will work. And after all this, I guess the manufacturers web sites might be next or tech support. Sorry I
did not have any real High Tech stuff for you.