ext. HD - System Profilers says Unable to list FireWire devices

Ok first off i have to say, i have encountered a very, very strange problem. I have purchased a WD My book Home Edition from eBay 3 days ago. I turned it on and connected it to my imac, via usb and installed all the files. (Wasn't really needed) So then i plug in the fire wire after safely removing the USB part. It doesn't recognize anything. I open Disk utility and nothing is shown for a my book. So i open System profiler to see if it is my firewire drive and it says -
FireWire Bus:

Warning: Unable to list FireWire devices.
Maximum Speed: Up to 800 Mb/sec

So i thought it was the drive. So i plug it into my Macbook via firewire, and right away it finds the drive. So nothing is wrong with the drive. So i restart my computer and reset the pram, and start it up. Again, nothing. So i came to think is it my firewire slot? So i plug in my camera via firewire, and it picks up right away. So im stuck in a VERY VERY strange frustrating situation and it seems its doing it for no reason.

Another thing i should add, I also have windows on my imac, so i booted up windows and i plugged in the firewire and again, nothing. But my computer does recognize something is plugged in. I am stuck.

Please if anyone here has any suggestions dont hesitate to help me!

FW 400 or 800?

does it work ok with USB connection? I had a similar problem with a WD drive and just started using the USB.

Yea the usb works perfect. Thats what its hooked with right now. The thing i dont understand is if i plug it in doing the following:
Unplug HDD power, unplug firewire, then connect power, connect firewire, it will show up as My book and then disappear. Im so confused.

i am having the same problem on my new imac. anyone else?