since it's happening on all 4 computers, i'm sure it's not an irq or similar problem. there has to be something the same with all 4 - in this case, here's my $2 diagnosis: the cable!!!!! yup, check and make sure the usb cable is okay. don't know if you can buy a usb to mini usb cable (never checked) but if you can, from best buy, or any other store with a GREAT return policy, you can check that at least.
also, sounds stupid, but make sure your wires are inserted properly and snugly. i know you said yellow to yellow and black to black - that's the biggest mistake i've seen others make (not doing that, actually). i had a hard time getting my connectors in - took far more force than i expected, and i didn't want to break anything. maybe you have the connectors upside down? or not seated well?
otherwise, you may have a bum unit.