Hello There,
A hard drive not recognized due to physical and logical damage.
- Any damage in the head, platters, firmware etc.
- Power surge
- Safely not removed can be one of the cause
- USB Port is not ok etc.
In the logical case, data can be recovered from software. But if the hard drive is not recognized that means you have to compromise with your data.
But you can check once with data recovery experts.
Note - Check that your hard disk is visible in Disk Management or not?
Hope it will help you!!