Vista won’t recognize USB external hard drives that work fine in XP

I have 2
Ezquest/Maxtor 500gb usb external drives I was using on my Dell machine running XP.
I got a new Vista (Ultimate) machine and, although it recognizes
the hardware
on both drives (& says they are “working properly” and
enabled), it says the drives are “unreadable”; it does not
recognize them in My Computer.
I tried to partition the drive thru control panel but there is a
red “+” sign
on the drive icon for the Ezquest and nothing happens when I click it.
(jut options for properties and help).
(I did the original NTFS partitioning on the XP computer). I reformatted under XP (where they still work fine and still Vista won’t accept them.

Thanks for any help.
rgs92g@gmail.com