We had a similar problem, one was Vista and external or the front usb port/card readers. I have a removeable one on my computer and use xp. As soon as I removed the card reader from the front of the computer it worked fine. My husband had to down load a work around for his computer and vista because he can't remove his card reader front usb ports. For some reason the GARMIN program sees these and doesn't see the GPS. Not sure if this applies to you but I haven't seen this option offered yet.