Cloning drives causes Drive signature collisions so it will not mount. Open Run and type diskmgmt.msc. Click Ok to open Disk Management to see if the drive is "seen" Open Command Prompt and Run as Administrator. Type the command  Diskpart to open Diskpart and hit Enter.   To change the disk’s signature and set the disk online, type the command unique disk ID= (New signature) where (New signature) is the new ID in hexadecimal. For example, you can set the new id as uniqueid disk ID= 1456ACBD. If you have given wrong format ID, the prompt will display the error:   When two storage devices have an identical disk signature, the secondary drive that creates disk signature collision will be turned offline, and cannot be mounted for use till the collision is fixed. Another way signature collisions can occur is with the creation and use of Virtual Hard Drives (VHDs). If for example a physical drive is converted to a VHD, or a copy is made of an existing VHD, then signatures will be duplicated and clashes can occur just as they do with physical hard drives. OR The sata operation for the drive is ATA or IRRT not AHCI or vice versa. You may be able to fix this using a Drive Dock via USB3  [URL] If this is a REALLY OLD IDE DRIVE use this [URL]  
Hi, I just finished setting up a new Windows 10 desktop. I opened the case and plugged in my old hard drive to the second connector to try to retrieve files. I can feel the old drive spinning, but the drive does not show up in file explorer. What do I do? (I only have modest computer experience, so hopefully, not too technical! Thanks.
File explorer will not see second hard drive