My passport does not appear on mac if Firewire is the connection

I bought 2 passport 400 GB with firewire connection for my Mac. They both work ok if connected via USB, but when I connect via Firewire using the cable supplied with the passport the Mac does not see it. Both disk, I tried to exchange cables (supplied in the box with the passport 400) and nothing change. Via USB is better than nothing, but because I work with big image files (100-110 MB) it is quite slow. Which is the reason for which I bought the ones with firewire connection.

I work with an Intel i.Mac running Tiger (OS 10.4). Any suggestions? 

thanks in advance , robert

PS sorry but english is not my mother language, I’ m writing from Italy

Have you tried contacting WD’s Technical Support about this? You can do so either by phone or email.

To Contact WD for Technical Support