Although a hardware failure is possible, its not likely. Also, a drive won't just "erase", I highly doubt some form of radiation, emp or whatever would have caused it. Static would cause a chip to fail before anything else, I don't tihnk it would just "erase" magneticly stored data. I guess it could, if it would hit the right spot but I can't even begin to think about how unlikely that is (even impossible I would reckon, the platters being surrounded by the casing). Anyways ...
No one will be able to tell you what happened, all we can do is take guesses. My guess is that either Windows didn't recognize the partition on it, due to drivers or BIOS config or something, connected it to a different port on your mainboard (different controller?) and/or you messed up somehow (sorry, happens to the best of us).
If you didn't recreate a new partition and have written new data to it, you could attempt to recover it. Often a driver/bios or controller issue is simply a matter of partition allignment. There are programs out there that can figure this out and recreate the original partition and reallign it so that windows detects it again.