I encountered the same problem last week for my WD My Book 320GB harddisk.
Error message: The disk in drive F is not formatted. Do you want to format it now?
If you receive such message, don't worry! I managed to find a solution via Google and restore my harddisk with intact data at no cost! The error is due to a corrupt boot sector and we just need to restore the backup files using a free open source software.
Step 1: Download 'Testdisk'
Step 2: Check out this website for a nice user 'Deleted090308' who share the solution:
A. At the first window, select “ No Log ” and press the < Enter > key.
B. Select which drive to analyse, choose “ Proceed ” and < Enter >.
C. Select partition type – Intel if it’s a PC then < Enter >.
D. Choose Advanced > press < Enter >.
E. Choose Boot > press < Enter >.
F. Choose Rebuild BS > press < Enter >.
G.Note: Do not need to choose Repair FAT, just exit the program. Computer should be able to recognize your hardisk again.
Hope the above help because it solved mine!
P/S I wrote to WD support before I found this solution. They recommended me to buy a data recovery software which cost US$49. If I have not been lucky at the web, I would have been so desperate to pay. Thus I decide to post this entry to share with everyone.