It has been a while but I believe I have had a similiar experience with an external drive. I’m afraid I don’t remember exactly if my external elements was seen by Windows Explorer or not, but I don’t think that it was. It could be seen as being recognized by the BIOS on bootup though.
This is what happened. One time when I was using the computer I could access the drive ok, then I couldn’t. Just like that it become unaccessable. I rebooted and I don’t think I could see it anymore in Explorer. My drive was a 1.5TB external Elements with no encryption and standard 512Kb sectors (before the new 4k sectors that are no being used). I removed the drive (it turned out to be a SATA II green drive) from the enclosure and connected it internally. Still was unusable and I don’t think even showing up in Explorer. But I have a copy of Spinrite 6 on a floppy disk and my computer has a floppy drive that I installed just to be able to boot off a floppy if I ever need to (like a Win98 boot disk with fdisk on it). I ran Spinrite and it found and recovered some sectors at the beginning of the disk. It started to read the rest of the disk ok so I terminated the program and rebooted to see if it had fixed it, and it did. I could read the drive ok again in Explorer. I rebooted with Spinrite and let it run through the entire drive. I think it took over 12 hours. Ever since I’ve been using the drive internally or in an external caddy. I’m hesitant to put it back in its enclosure. Spinrite is rather expensive though (about $80) but it has recovered other drives for me, too. I have different drives that I swap in and out of my computer that I boot from or just for data storage. Just about I week ago I was able to recover an old 160GB IDE WD hard drive I sometimes boot Win XP from that all of a sudden kept rebooting after displaying the Windows XP logo. The microsoft knowledge base helped me determine that the registry probably wasn’t being read correctly due to a bad or corrupt sector. Spinrite fixed it. I know I probably sound like a advertisement for this software but I have no connection to it. Just relaying my experience. (Spinrite at www.grc.com))