My computer randomly reset but I still have all of my files?

Sorry if it isn't too clear, but English isn't my first language and I am quite unnerved right now. I turned on my Computer and it took a while, which is weird since there was no update since I last used it two days ago. When it turned on it was like "new", it has a default background and the desktop doesnt have any of the folders. Yet I still have all my apps. I checked on the folders like Download, pictures, documents etc... and they are empty. BUT I also checked on This PC>Windows (C:)>user and all of my stuff is there. But why? What could have cause it and how can I risolve this problem and prevent it from happening in the future?