The causes are mostly user`s mistake, virus, bad sector, and electric shock that causes series viruses, and bad sectors, that deletes every information(dividing the partition in many ways).

Except the reasons above, if there is a problem with the partition table itself, the recovery rate is 90~100%.

Mostly it will indicate “ Invalid Drive Specification ” .

Usually Disk Utility is used but if the cause is a Bad Sector or Virus etc, it is almost impossible to fix and recover the data.

If you deleted the partition by mistake you can try to fix it yourself, but if you don`t know the reason, it is safe to contact and council with a professional recovery company.