Thanks again milsabords, the unit does indeed have a separate power supply and powers up OK. I am aware of the need to power it up before switching on the PC, unfortunately to no avail. It works fine with the USB connection, if somewhat slow and limiting in functionality.
I spent a while on a 'chat' with Iomega technical support and believe it or not their only suggestion was to try a different cable and and PC (no mention of powering up before switching PC on, or checking BIOS), when I said I had neither they offered to change the hard drive. I don't think this is the issue though as I had a friend load 100MB+ of video using his PC and cable as he has the same hard drive.