Follow these steps to troubleshoot a FireWire device that isn't working.
Make sure all FireWire devices are turned on and all cables and power cords are plugged in. Make sure the cables are no more than 15 feet (4.5 meters) long and that you haven't connected a device to the computer in two ways.
Be sure you installed any software that came with the device. Check the manufacturer's Web site for the latest software.
If the device still doesn't work, try quitting and restarting any applications that use the device.