Vista - Vista SP1 - Missing Hard Drives

My PC is a very souped up quad-core wtih 4GB RAM and an nVidia GTX card, an
800w power supply to handle all necessary accesories. I also have a 5 year
old Compaq PC that I was about to throw out. However, the new PC which has
Vista Ultimate has problem recognizing my external drives. I ave 2 internal
drives, a Seagate 500GB and 1TB drives that are recognized and work like a
charm. The problem is that I have 2 Lacie Mini External drives that Vista
recognizes, but a few minutes after accessing the drives they disappear,
sometimes together, sometimes one at a time. Once they disappear, they go to
the 'unknown device' section in the Device Manager and when I click on them
Vista asks for a 'driver update', but the problem is that these drives, like
many other drives, do not come with drivers...once you format them, under XP
and Vista, they automatically work. I used these drives for more than a year
under XP and NEVER had a problem. and when I attach them to my Old PC, still
no problem....I installed SP1 for Vista, and still the same problem...I do
see that all over the Internet other users are having similar problem too
(with Vista having major issues with Firewire drives or accessories), but no
one has come up with a concrete solution. Can anyone help?