ha! i'd been having trouble with my sewing machine back before i moved, and a while back i chatted up a sewing machine repair guy in a local fabric shop and he had some suggestions for basic troubleshooting and i finally got around to setting the machine up and rethreading it and checking all the various knobs and twiddly bits and it seems to be working fine now. so whatever the problem was, it appears to have been a loose nut behind the machine because with all the threading and bobbining done right and settings set, it appears to work. yay!