Recently had a four year old Mybook World edition fitted with a 1Tb drive that had been working non stop until it keeled over with the same fault, data was intact but the control logic had died. The on board interface for some reason kept reporting that "Drive A Has Failed" but was able to access it's Linux based operating system on a separate drive partition. A strange fault this, almost as if the Mybook was selectivly blind to what it was connected to.
There is a way to recover the data with little expenditure, I managed to recover all my stuff (some 400Gb) but you need a PC that is SATA based in order to be able to plug in the HDD and access the stored contents.
1) Download from the internet a copy of Puppy Linux and burn it onto a CD as a bootable operating system.
2) Remove the HDD from the defective Mybook.
3) Fit the HDD to the SATA based PC, both power and data leads.
4) Insert the Puppy Linux bootable distro into the PC's CD drive.
5) Instruct the PC to boot from the CD, you may need to edit your BIOS settings for this.
6) Allow Puppy Linux to boot up from the CD and mount the HDDs in your computer and the Mybook HDD
7) In Puppy, open the Mybook HDD into a Window, look for a suitable destination HDD on the PC and open that in a seperate window. Note that if the drive is really shagged, this is final confirmation that you will not be able to view the contents and need to break out the kleenex.
8) Drag and drop copy (hold CTRL) the files you want to save from the Mybook HDD to the destination HDD. Note that some filenames may be unusual in length and may have to be renamed during this process.
9) Once complete, shut down Puppy, turn off the PC, remove the Mybook HDD.
10) Restart your PC, and back up your recovered files to a new source.