Partition loss from Windows is not at all a common data loss issue. Once a partition went missing, all data stored on it could vanish forever, unless you act soon. If there is nothing important data present in the lost partition, then you can create a new partition or repartition your hard drive again.
If your lost partition holds lots of important data, then it is sure that you are in serious circumstance. Yet, don't need to be panic. As every problem has its own solution, even the lost partition can be recovered using apt techniques.
Situation 1: When Boot Partition is Lost
It is the known fact that your system cannot boot if the boot partition is lost from Windows. All you will see is a blank blue or black screen at the startup. At this stage, you need to try accessible ways to boot your computer.
And, here it is described a method to boot Windows after its boot partition is missing. (Applicable for Windows 10, 8 and 7 versions).
Caution: If you are missing the partition other than boot partition, then don't create any new partition, as it overwrites the lost partition.
Situation 2: Partition other than Boot Partition is Lost
If your boot partition is un-intact but other partitions that hold your personal data are missing, then it really troubles you.
But, no qualms! You can easily recover the lost partition using Remo Recover (Windows) software. This is an assured way to restore your lost partitions in few mouse clicks. This robust tool can locate even your inaccessible partitions that are corrupted/damaged and retrieves data from them easily. Supports recovering of data that are lost due to partitioning errors, corruptions, etc. Recovers data from formatted partitions, even after re-installing Windows, compressed files from NTFS or FAT formatted drives etc. Not just lost partition, it can also recover your hard disk data after hard drive crash or if it fails to boot due to any issue. Supports restoration of lost partition data from hard drives (SATA / SCSI / IDE) and USB external hard drives. Allows you to store recovered data onto CD / DVD or to any accessible drive in a compressed format to save storage space.