Not sure if this helps you, but I had a similar problem. I am using Maxtor One Touch II and one day the device suddenly cannot be recognized by the OS. I was copying some huge chunks of data with firewire when the problem occurs. Since then, the maxtor cannot be detected by the OS. I have tested it with my home PC, my sony TR and my office computer and the result is the same. I called up Maxtor and got their assurance to break the warranty seal so that I can connect the 300GB hdd to my computer via IDE and that works. That’s how I managed to “recover” all my data. :D
The problem was due to the chipset in the Maxtor One Touch II being corrupted. They replaced the whole unit for me. Anyway, I had stopped using firewire on this bugger since then. Good luck to you.