Usb device attached & working in cmd, but not in explorer

"According to this forum post, it could be a slight mismatch of drive letters for Zen Plus in windows.

I figured it out. What I had to do was connect my Zen and go into the disk management utility - right-click on My Computer and click Manage. The zen should appear as a drive. Right-click on it and select Change Drive letter and paths...
Change the Drive letter to a free drive and click Ok. It should work immediately!

Also, you may consider updating your pc's USB drivers. Be sure to make a system restore point before (even though this would probably be done automatically)"