Has this drive ever worked before on either computer? And which OS are you running?
I've recently hit an issue with one of my generic hard drive enclosures. In windows XP and on my mac no issues. But since upgrading my desktop to Win 7, it keeps coming up with device isn't recognised when using the Firewire port and very very very slow performance if any response when connected by USB. I suspect my issue is a driver update is required. Wondering if you are in a similar position?