jigsawbill.
The only problem that I see that it could be is that the External Hard Drives are formatted with FAT or FAT 32 and the Windows 7 machine is formatted with NTFS. When you plug the external drive into the win7 machine it wants to format it with NTFS. You may need to format them with NTFS in order to use the drives with Windows 7.
Thank You,
Dell-Jesse L
Dell Social Media and Communities