Hello,
Thank you for posting in Q&A forum.
There are several possible solutions to your problem that you can try:
Check for driver issues: Try uninstalling the driver for the external hard drive in Device Manager, then reconnecting the hard drive to have Windows automatically reinstall the driver.
Try using different USB ports: Sometimes the problem may be with the USB port, changing the port may solve the problem.
Create a new volume in disk management: As you mentioned that the hard drive is displayed in disk management but not allocated space, if all options are grayed out and not available, it may be because no space is allocated to the hard drive. Normally, right clicking on unallocated space should give you the option to create a simple volume, but you mentioned that this option is not available. This may indicate damage or other issues with the hard drive.
Using the command line: If the options in disk management are not available, you can try using the diskpart command to clear the hard drive and create a new partition. Note: This will delete all data on the hard drive.
Open the command prompt (as an administrator).
Enter diskpart and press enter.
Enter a list disk to view all disk numbers.
Find your external hard drive number based on the displayed results, and then enter select disk X (where X is your hard drive number).
Enter clean to clear all partitions on the hard drive (note that this will delete all data).
Afterwards, you can return to disk management and try creating a new volume.
Try connecting to another computer: This can determine whether the problem is on the hard drive or on your computer.
If none of the above methods can solve the problem, it is likely that your external hard drive has a hardware malfunction and may require professional repair or replacement.
Hope this answer can help you well.
Best regards,
Jill Zhou