In the setting of AutoCAD options (options) in the File tab (the leftmost tab) there is a path autosave. There AutoCAD saves temporary files, usually with the extension ac $ (in the tab opening and saving) .You must look for it. Generally, if there are files, they can be found by date, and they can be seen the empty volume or not. To open them you need to simply rename, appending the extension DWG. the same can be done with the files with the extension bak. And yet there is a command in AutoCAD recover it allows you to open corrupted files. As last resort use
Recovery Toolbox for DWG : http://www.dwg.recoverytoolbox.com/