It had been connected partitioned as 2 disks to a Vista PC for a while and worked fine. It was set up as RAID 1, so the 6Tb appeared as one 3Tb. One partition was 2TB and the second is 1Tb. It worked fine.
I got rid of the Vista PC and attached it to a new Windows 7 PC a year ago. Now Disk Management lists it as not having any drive letter, Healthy (EFI System Partition), and it is not initialized. The space is unallocated. I cannot get the two drive letters to appear. It has never appeared when connected to the Win 7 PC; I just got around to troubleshooting it now.
It is connected to USB in the back of the PC.