Is it a USB 3.0 one? I have a Iomega 500GB 2.5 HDD and the cable that came with it has both 2.0 and 3.0 USB ends on one cable(if you get what I mean). Anyway, each time I plug in the 2.0 end of the cable in both of my PCs, I see the light on the HDD and I hear it spinning up but nothing comes up(and yes, it's a 2.0 USB port). When I plug in the USB 3.0 it works. So, if your cable is like that, why not try using the 3.0 end of the lead.