Oh, yeah, before I forget: I had another external HD scare on the other day. It wouldn't mount; no partitions showed from it. This was the HD I have been restoring data from.
tl;dr
I had it plugged into a USB port that was subtly damaged. Non-power-requiring devices worked when hooked up to it, but this HD needed to draw power from it. The HD (hard drive for those not in the know) mounted when I plugged it into the other USB port.