There a few possible reasons why a hard drive would not be detected. The drive may be using a unsupported format. The hard drive must be formatted in either FAT32, exFAT or NTFS. The Mobilelite Wireless does not support MacOS or Linux formats. The partition type could be GPT. This partition type is usually only used for boot drives and connect be read by the Mobilelite Wireless. You will need to change the partition type to MBR. You may have some type of security feature enabled on the drive. This could be some type of encryption or password protection software that came with the drive. This must be disabled.