Hi there xrklkx,
As you've already taken the drive out of the enclosure, you can attach it internally to a desktop system with SATA & power cables. That way, you will see if all of this is caused by the enclosure or the cable.
Keep in mind that his may not work in case the device features hardware encryption or has proprietary connectors.
If the drive gets recognized when installed internally, you can try to access it right away. If you can't do that, you can see if some data recovery tool will do the job.
If the drive is nowhere to be recognized(check Disk Management), then you will need to contact a data recovery company, if the data stored on the drive is really important.
You should keep in mind that the important data should always be stored on at least two places.
Let me know how this goes,