the many post addressing your exact problem.

You can try attaching the drive to another system
Try other USB Cables
Try the drive in another enclosure
Try the bare drive inside the inside the system case. (laptops excluded)
If those don't work....there's data recovery services that will be glad to take your hard earned $$ in hopes of recovering your priceless data..

Only then will you realize a single data source with no backup is really a bad data management model.