When an external drive "goes bad," it can be either the drive itself or the electronics in the enclosure at fault. Was this a Western Digital external drive? WD's external drive enclosures and the proprietary bridge chipsets in them are real junk. The drives inside are much better than their "packaging."
Many, if not most, Powerbook-G4-and-USB-drive combinations relying on bus power don't supply enough power to the drive. The result is that the drive
appears to be powered, but it can't be used. I don't think that was your problem, or not your
only problem, because plugging your drive into a powered hub didn't resolve it. So I suspect the bridge chipset in your enclosure failed.