I'm not sure why unhooking the fan would cause the enclosure to not function at all. Is there a way you could move the fan out of the way while still keeping it plugged in? It all seems a bit odd to me. First, I would try setting the drive to master, and if that didn't work, try Cable Select. After that, I would try a different drive, and repeat. I'm not sure, but I doubt it would have issues with the capacity of the drive being too large for it to handle. I'm assuming the drives you are trying to use already work in some other machine before you tried them in the enclosure. Also, make sure that the Firewire port on the computer functions properly with other devices.

Did you try the things they say in the Mac FAQ file on their site? It specifically says that if you are running OS 8 or 9, you need to use the included disk (Hard Disk Speed Tools software) to format the drive. Also, they discuss how to deal with the dreaded Firewire bridge board problem.

Right now, those are the only things I can think of right now that would be causing you problems. Failing that, I would assume that the enclosure itself is the root cause of the problem.[/i]