I too am having unexplained problems with Maxtor One Touch II external hard drives.
I have a Dell Inspiron 8500 with a port replicator. I had the drive go unallocated 3 times before I finally gave up and returned it to the store. I swapped it for another drive, plugged it in, formatted the drive and copied my My Pictures folder for backup and then Ghosted my laptop to the external drive. In this instance I never disconnected the drive frm the high speed USB port or the power although I would shut the drive off when it was not in use.
Last night I shut down the Laptop and forgot to turn off the hard drive. Today I docked the laptop, turned on the computer and no external drive shows up. Drive Managment shows the drive as unallocated again.