You can't use the USB cable on a FireWire camcorder to transfer video to the computer. Connecting the camcorder to the computer via USB only allows you to transfer pictures. If you have the A/V cable that came with the camcorder you can connect that to a video capture device and the capture device to the computer via USB. I have four older Sony camcorders (three use mini DV tapes) and none of them will allow me to transfer video to the computer via USB. You can try adding a FireWire card to your computer. If you are using Windows 10 you will need to download a legacy FireWire driver.