Hey there, cycloneticz.
Have you had any issues with the HDD itself prior to this problem?
I'd recommend that you try the drive with a different computer, to see if the same thing happens. It would be even better if it's a desktop computer, so that you can try the drive internally via a SATA connection. Check if the enclosure has any drivers which you need to install in order for it to be properly detected and speaking of which, make sure that the enclosure itself is detected in Device Manager. You should also check if the enclosure supports the capacity of the HDD.
Please let me know how everything goes.