Problem with Verbatim SmartDisk Firelite used for backup

I have used the Firelite disk for back up for 15 months with no problem. Then suddenly my G5 would not recognize the disk (icon did not appear on desk top and Time Machine would not work). If I shut down the G5, unplugged the disk from the firewire port, restarted the G5, and then plugged the disk in again, the icon would appear and it would back up fine until I shut the G5 down again. After a couple of weeks, the computer would not recognize the disk even after shutting down and restarting the G5. I took the disk and cable to an Apple store where they plugged it into a laptop (apparently the type of firewire port the disk uses no longer is available on the new IMacs) and the icon appeared on the desk top and the files were accessible, apparently meaning the disk and cable are OK. I brought the disk home, and when I plugged it into my G5 now, the green light on the disk that shows it is powered up no longer lights. That is a first, it had always lit even when the icon did not appear on the desktop. I tried the process mentioned in another topic here, turning off all power to the computer for a few minutes, and then plugging it in again, and that did not work. Any ideas?