How do I reformat an unmountable/unrecognised/unformatted USB drive?

Solution 1:

Not sure, but can dd command be of any help?

http://hints.macworld.com/article.php?story=20050302225659382

in Windows Vista or higher, you can try to format it with diskpart.

Open a cmd.exe with administrative privileges and type "diskpart".

The command "lis dis" lists all your storage devices. If your USB stick is on the list (e.g. device number 3), you can select it with "sel dis 3".

Then you can reformat it with "clean", "create partition primary" and "format fs=fat32 quick".

For additional information see https://support.microsoft.com/en-us/kb/300415