You've tried it on more than one system with the same issue? The drive has failed. As long as you don't try formatting and creating any new data on the drive, there's a chance you can still grab what was on there. The most reliable way would be to connect it directly through SATA on to a desktop motherboard (disassembling the enclosure and using the drive's own SATA connection), as there could also be an issue with the controller board of the enclosure you're using. I recommend Restorer Ultimate, it's not freeware but you can probably download it somewhere with a few Google searches (I did). Basically you need to scan the drive where the partition is missing or damaged (the 1.5TB one) and let Restorer try and recreate the RAW files into readable ones.
As for using the drive again: don't. If the drive has failed like this then it will do again, and you'll have to go through the same painstaking recovery procedures that always have a reasonably high chance of failure
If you really want your data and you have no luck with Restorer or similar high quality, reputable software, then you are going to be looking at a data recovery center which will cost a lot, and I'm talking £££, sometimes 4 figures for badly failed drives.
A word of advice:
Always keep at least 2 copies of anything important on separate drives, not partitions, because HDD failure is a lot more common and expensive to recover from than many people think.
Cloud storage is not a bad option as well, they have the same kind of redundant backup drives for this kind of situation!