Did it work formerly with the very same computer and OS that now fails to recognize it? If not, it may be an issue of the OS and the file system support.
Trying with a different computer is certainly worth the effort.
I bought an adapter ages ago for about $/€/£40 that connects "raw" HDs of various interfaces to USB; it works, if the HD is intact. If the fault is with the USB adapter in the drive case (– very rare!), this is the remedy. You can ask around if someone in your vicinity owns such a device; the main use case is to save data from old computers.