A friend of mine bring me an external hard disk that suddenly become undetected and after further investigation, I found it’s unallocated.
Because too many important files, I need to recover the partition as it is, without losing any data.
After browsing many sites, I found the freeware partition software that could recover the lost/damage partition. it’s called MiniTool Partition Recovery. If you experience the same problem, you can use this software and the complete HowTo guide from this link http://www.minitool-partitionrecovery.com/recoverymore.html.