Memory disappears on the wrong hard drive/ is missing and untraceable?

On my SSD hard drive, which also contains Windows, I can't find about 50 GB of files. The PC claims that there are 50 GB of files in the "Users" folder or its subfolder "Admin," but when you open the folder, all the contents are only 1.5 GB. Where is the rest? I'm currently having a problem where whenever I open and play a certain game on a different hard drive, the remaining memory on the SSD that doesn't have the game on it decreases until it disappears, and then the game crashes. What's causing this?