There is a list of reasons why your system stops recognizing the hard drive.
Sometimes, it reports that the media disk is write protected or it might tell you to insert a disk even though it is inserted.
This error may occur, when you try to insert a USB drive or external hard disk.
Sometimes, it may report problems such as can't read or unable to detect the hard disk.
Mentioned below are some of the general tips for troubleshooting hard disk detection issues.
However, you need to check, which one can be applied to your case.

1. Running windows update can be the solution of your hard disk detection problem.
   
2. Remove each and every one of the old USB hard disk drivers.
   Now, you can install new device driver for hard disk reading purpose.
   Old drivers can confuse windows and hence, causing to display messages like 'drive letter conflict' or other reading issues.
   
3. Use AC adapter if you have one instead of using the USB port of your system for charging various handheld devices.
   It is highly recommended to rely on AC adapters
4. Plug-in your laptops in the AC power in order to give enough power to run the disk correctly.
   
5. You can test your hard drive on different systems to test the functionality of the system whether it is working correctly or not.
   
6. You can try by using a different USB cable to connect your hard drive to your system.
   
7. If your hard disk is having its own AC adapter then you might have to restart your system in order to detect the hard drive.
   
8. If your hard drive depends upon the power from the USB port itself then sometimes you may not get enough power voltage.
   In this case try connecting your hard drive to a self-powered USB hub.
   
9. If the hard drive is being shown in disk management, but not in 'My computer' then you can fix it easily.
   The problems may be due to bad sectors so you can give it to the manufacturer for removing bad sectors from your hard disk.
   This problem may also be due to unallocated or unassigned drives.
   You can go to the disk management and assign a letter to this unallocated drive in order to get this drive on 'My computer.
   '
10. If only the hard drive could not connect and other devices like printer and mouse are working properly then you might have to check whether the hard drive drivers are disabled.
    
11. If none of the above methods are working then try once the steps mentioned below.
    

-Shutdown the computer and unplug it from the wall.
Remove the battery or the other power source in case it is a laptop.
-Remove all USB devices and disconnect the power sources of the USB drive too.
-Now, after few hours start the whole thing properly.
Sometimes, this might be the solution for hard disk reading issues.