External Hard Drives Shut Off When Another Is Turned On

Hi,

I have Windows XP Pro, SP2, IE7.

I have a number of external hard drives. I have no problems with any of them except for 2. They were purchased at the same time from the same supplier. I called them several times about this problem and returned them 2 times for "repair" but they came back with the same problem. When one is turned on and I turn on the other one, the first one will shut off. If I turn it back on, the other one shuts off. They both can't be on at the same time. I can have 9 other ext hdds turned on at the same time along with only 1 of the 2 problematic ones and there's no conflict with any of the others.

I tried connecting them different ways. I had both of them on 2 different hubs but I changed it so one would be on a hub and one would be connected directly to my tower. That didn't work. I then connected both to my tower and that didn't work either. I changed the drive letters (to drive letters that have never been used) of each of them when the other one was turned off but that didn't work.

Can anyone help?

Denise