Problem with WD 500 GB My Book, Can't see files

Ok experts this is pretty unusual. It had been about six weeks since I last accessed the files on this hard drive. Connected to the computer and I could see the drive but none of the files are showing up. I had about 300 Gb of information stored but now Windows reports 465 Gb total size and 465 Gb of free space. It's as if the hard drive has somehow reset itself to the factory configuration all on it's own. I have scanned the drive using Restorer 2000 but still can't see any of the data I had added. I know the files have got to be on the disk somewhere. Could this possibly have something to do with a lost or corrupted FAT or MFT and if so any ideas as to how to access my data. Please help

 

Provide OS you are using as this may be important to what steps to take. Thank you.

 

WXP Home Edition SP3