First thing to do is reboot and try again. Do you have a firewire? I download via firewire, and I've never had a problem, so if you do, that's faster.
Obviously it's a computer problem when both cameras are not recognized. Do you have any CD's with drivers or anything? If you do you might want to check that.
Also you might want to change usb ports, and try another one too. Pull out and put back in the USB cable. Try another USB cable too.
Sorry for all the questions, but there are so many possible solutions.
Chris