Did you try the software titles noted at the top of this forum (Lost and Found.)
Yesterday my computer (runs ubuntu) read my WD My Book just fine. Today it didn't and neither did my windows machines. I took apart the drive and put it into an external enclosure. The computer reads it as a mass storage device but explorer doesn't see it. If I go to Disk Management it is not listed under the C drive but it is listed in the pane below where it lists Disk 0, Disk 1, Disk 2, etc. Any thoughts on how I can get explorer to read it?