https://en.wikipedia.org/wiki/Head_crash
Hope you have back ups on other drives.
I had an external hard drive that failed which I kept all my pictures I've ever taken on. Thought I lost everything forever. Amazingly a local computer repairs shop was able to recover most of the data for $120 during a time span of 3 days. One of the most stressful times ever. Take your computer to a shop. They are most likely the only ones who can recover your data if its at all salvageable.
This is actually quite scary, I've spent tons of time collecting almost a gig worth of research!