I have an external iomega drive.. I can hook it up via the firewire port on my notebook computer and it works fine..
I have copied data to it with no problems..
If I hook it up to my desktop via usb (no firewire on the desktop), it recognizes that hooked up a device ("ding dong!"),
but it doesn't assign a drive letter.. If I go into the drive manager, I see the drive listed but it says it is empty and only gives me the option to create a "new simple volume", which I assume will wipe the drive..
Have you tried to assign a drive letter manually?
Right-click the appropriate ribbon in Disk Management.
Choose "Change Drive Letter and Paths"
Click "New" and choose a letter from the drop-down alphabet.
Hopefully, it's description will then change in Disk Management and you'll be able to access it.