Your symptoms are consistent with data corruption, or a drive that has been reformatting with a different file system on another operating system.  Do you need access to the data? 


If so, some software applications may be helpful in situations where the drive hardware is seen, but the volume is corrupt. A couple examples are www.stellarinfo.com, www.binarybiz.com, and www.prosofteng.com. There are many companies that provide these services, it is best to be selective. This email is not a referral or recommendation as we are not affiliated with these companies in any way. 


If data recovery is not necessary, you can simply reformat the drive per the instructions in your product manual.