Hi there skynet user,
Have you tried something simple as just changing the cable?
If the problem persists even with a different cable, then there is something wrong with the enclosure or the drive itself. You can try connecting the drive internally and see whether it will get recognized. Keep in mind that taking the drive out of the enclosure most probably will void the warranty.
Your other option is a data recovery company as i7Baby already suggested.
Cheers,
D_Know_WD