Wow, I was working on my friend's external HD that had the same exact problem. Jae even stepped into help but we both concluded the partition took a dump. It also didn't show up on the desktop and the only evidence that the computer sensed it was in the BIOS and the Drive Manger classified as a "Disk Drive". I even cracked it up open and connected it via IDE and it still didn't work

What kind is your mothers?