My ZEN is acting weird regarding that, too. It kept randomly shutting itself off, so I reset it. Now, when I try to connect it to the computer, Windows 7 recognizes that a device has been connected, but the ZEN doesn't seem to want to mount as a portable HDD.
As it is, I'm just treating it as though it's bricked, since it won't do anything. It lasted 1.5 years, so not too bad, I suppose.
Of course, I never backed anything up, so when I get a new MP3 player, I'll have to redownload everything... Yay.