If you accidentally delete partition on a disk, you may recover it with MiniTool Partition Wizard, one of the best free partition manager.
Note: It is important that you do not write any data to the hard disk or format after you notice the problem. Otherwise, there is a chance that you could overwrite data on the partition you’re trying to recover.
In this video, I will show how to recover lost partition on D drive with MiniTool Partition Wizard (free edition).
Warning: I won’t responsible in any damage or failure that may happened if you’re using this tool so use at your own risk.
MiniTool Partition Wizard
If you can’t recover partition with this tool, you can try TestDisk.
Recover lost partition on Windows 8.1 with TestDisk
If you want to recover only some deleted files, you may want to check this video.
Recover lost files on Windows with Recuva