Just bought two new USB 3TB drives model [Deleted]. The drives could not co-exist on the same machine one loaded directly the other never came up on Win7 or Win8 both 64bit. After some sleuthing I found out that one drive was offline which I changed to online after which they both load and and coexist happily on any of my machines.
Apparently the two brand new drives had the same signature form the factory. The drives were manufactured in two different plants one in Thailand the other in Malaysia. Clearly this is a problem that should be corrected in the manufacturing line, and maybe a solution for the problem should be highlighted in the FAQ ad most users would probably have no clue how to fix this problem.