External drive was readable, now it is unallocated?

Hi all,

The situation is fairly simple. This morning I :

1: Unmounted and unplugged my external drive which is a WD My Book Essential 2TB
2: Took it to a colleague and tried to connect it to his IMac4 which has OS X
3: Nothing worked, we could see the drive but couldn't access it even with the help of somme tools made for that.
4: Took it back home, plug it in....nothing. It doesn't show in My Computer and according to Disk Management and Paragon Partition Manager the space is unallocated.

What do you think is happening?

Thanks

What tools did you try on the Mac to make the drive readable?

The Paragon thingy and 3G something

I'm talking about your step #3. It is possible you used something on the Mac that unformatted the drive.

Is that what it is then, it was formatted?

Nope I don't see how something could have formatted my drive, I happen to be a retired network tech so I know a thing or two and believe me we didn't do anything wrong.