A partition is the space defined on your hard drive to be used for the system or for storing data. Most of users prefer to split a hard disk into multiple partitions in order to organize their data more effectively. For example, you may set many independent partitions for different use: one partition for operating system, one for documents, one for programs, etc. Partition lost is inevitable for ever computer users. If your partition is lost, missed, or deleted, you may find the vital or important data stored on them also disappeared. Is it possible to recover a lost partition? Or recover the data on lost partition? http://www.diskgetor.com/lost-partition-recovery.htm
When you could not see one of your partitions that means might be corrupted or lost, and of course, the data store on them cannot be accessible, too.
The partition lost may happened after operating system reinstallation, accidentally deletion, incorrect manipulation, virus infection. Partition lost most because of partition table corruption. Partition Table is a kind of system file which contains critical information about the hard drive partitions, including the start point and end point of an external hard drive partition, file system, name, size and other important information of an external hard drive partition.
Like I said, the partition table could be damaged by operating system reinstallation, accidentally deletion, incorrect manipulation, virus infection, hardware problems, etc.
Use diskgetor data recovery software, There is nothing to worry, because when you lost a hard drive partition, you are not initially lost everything but just the parameters that mark how the partition is setup.
However, to restore the partition you will most likely need to reestablish those parameters.
more info check http://www.diskgetor.com/