This happened to my girlfriend a few months back. Being an IT specialist, I had no idea what could have happened.
However, I ran a few things to find out what was using all her space (since I noticed her disk space was running high).
It turns out that the iPhone backups had been saved for about 4 years, 100GB of it. After deleting these, the library magically appeared. It might be tied to this.
I would suggest looking at your disk usage on your laptop and see if clearing out a few large, no longer needed files will return it back to life.
There is no way to know what happened to your files unless you just do some simple trial-and-error steps.
Also, run a disk check on your hard drive. If it's more than 4 years old, it's prone to dying anytime soon.