How do I repair a hard drive that was being written to while my MacBook Air crashed? (Drive will not mount)
I'm assuming that the port in your macbook air has been confirmed to be in working condition. Another consideration is that the hard drive's port has been damaged.

Are you able (perhaps through a friend) to test the hard drive functionality on another mac or windows system? Even if you had to reformat on a windows system, that would (hopefully) get the drive functioning, and then you could thereafter reformat for mac.