I have very similar issues...My PCis 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 control panel 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 SP! for Vista, and still the same problem...I do see that all over the Internet other users are having the same problem too, but no on has come up with a concrete solution. Can anyone help?