Hey dude! Replying on here since you sent this over Twitter to me.
If your new HDD suddenly started throwing tons of errors and wouldn't unlock, despite previously doing so and working, it certainly could have died in the midst of you using it. I had a friend of mine have something similar happen, but he was using flash storage in his hardmodded console. He had swapped it in, set it up, all was well, etc. After several hours of transferring games over FTP the transfers came to a standstill and tons of errors were produced. Upon restarting the console, he couldn't successfully boot up. Determined the storage had died mid transfer.
You're using a HDD in this case but that can happen with new and old storage. If your stock HDD works just fine, there's nothing wrong with the console. Again, it sounds more like your new HDD is the culprit, especially since it all worked before and now can't unlock properly.
For future FTP transfers I personally limit my transfers to 1 connection, 1 file at a time. In my experience I'll get errors, incomplete transfers, and overall a bad experience when I try to transfer more than 1 file at a time to a console.