Hi, I happened to read your post. Sometimes back, almost exactly same thing happened to one of my clients as well. Here's how we figure out what is wrong and what exactly is causing such:
Click on your HOME and see if there is any OLD USER folder resides. Trash it.
Click on your DOCUMENT folder and see if you have any old VM fusion related folder still exists. If yes, trash it. Why? Because OLD virtual machine may still be residing in a folder and that occupies a lot of space.
Now, right click on every folder of your DOCUMENT FOLDER and check the info to figure out if any one of them contains with massive space. If yes and you won't need that, trash it.
Now click on VIDEO and repeat the same info check to make sure if some Movie Events or Projects are repeated and are swallowing tons of space.
Same thing applies in the MUSIC folder. Restart and see the difference.
Once these primary steps are applied, you can still see where more space being missing by following the secondary solution:
First of all be sure that your HD space has not been misreported. The approximate space as you see left is what it should be approximately at the point of your reading. Don't get me wrong. Let me simplify it and give you a quick fix of this issue.
How? I assume that now as you are reading this, you are in the same Mac and have the same issue. Now please click to Application folder, click to Utilities and click on Activity Monitor.
Once the Activity Monitor opens, find out which is the App or Process that is hovering Gigabytes of spaces.
Once you figure out that some Apps or processes are using extremely high amount of spaces, just quit them or force quit them. Done!
Now to make sure that it won't repeat, click on Apple logo, click on System Preferences, click on Users & Groups, click on Login Items, and then kick the unwanted items out from there by checking on them and clicking on "-" button. Restart your Mac.