I had a problem a while ago with my 40 gig Western Digital HDD.The problem seems to be the same: sudden loss of data, no label on my drive. I took out the cover on my box checked all the cables and powered on my computer. As it powered up I started hearing strange noises from my drive as if the drive is trying to spin up but failed and retried again a couple of times. I started moving the power link to the HDD and finally it booted. Of course all of my data was still lost. I recovered all of my data with
GetDataBack which worked like a charm but a few days ago the same thing happened again (the spin up failure) this time without data loss. I digged around and found out that a friend of mine had the same problem with a HDD identical to mine so I concluded that the problem must be with the HDD. I think that there is a shortcircuit in the power socket which stops my drive from spining up (not only ant power up but also while using my computer normally since I experienced lock-ups while trying to access the drive accompanied by the same spin up sounds). I am seriously considering changing my hard drive manufacturer (since I have another 80 gig WD HDD). Hope this helps you solve your problem.
Good Luck