I have this problem regarding one of my hard drives. Every so often I lose access to it in Windows Explorer for no apparent reason. Also I have now put it in a caddy and if I pull the drive out and back in, I also lose the drive! Even if I click on 'Scan for Hardware Changes'.
I don't know whether it's a problem due to a failing drive or it's some sort of power saving feature or it's an issue with Windows 7.
The drive is a Western Digital WD10EADS Caviar Green. It's less than a year old too!
Anyone have this drive with similar issues?