|Go to Device Manager and see if the Enclosure is showing there. The enclosure must be identified in order for the drive to show. |
If the enclosure isn't showing in Device Manager then you other option is to remove the drive from the enclosure and connect internally. This, of course, is only possible with an desktop computer that can handle the type and size hard drive you have.
In your case you may want to temporarily try the drive internally on a friends computer. The parameters that I mentioned above still apply.
If the Enclosure doesn't show on multiple computers that would be an indication it is defective.