My storage says it's full but it isn't.

My storage says it's full but it isn't. I've deleted things. I backed up to ext hd. My projects refuse to locate data. Even though I was pretty sure I program managed the projects to keep the material in the project but even if I hadn't - I'm looking at the files and to won't find them and I have to keep starting projects over. It's very frustrating and I can't use your product because It won't work.