Western Digital My Book Files Missing?

Hello everyone, I recently came across this site and I am in need of some help please, any suggestion appreciated! I have owned a Western Digital My Book 500gb external hard drive for some time and never had a problem with it. I usually turn it off when its not in use and use the regular hard drive for file storage. The last time I turned it off I received an error message along the lines of - F:/MyBook/Recyler/hfhsh... has lost data which might not be recovered. Upon restarting the drive, it appears to be empty and asked to be formatted before using. Does anyone know how I can restore my files, they mean so much to me and I must get them back, I appreciate any help possible!