Microsoft Office has a fantastic feature called AutoSave; that it can automatically save a temporary PPT copy on a periodic basis. The feature is turned on by default and the default save interval is 10 minutes. And AutoRecover, a feature that is available in some Office applications, attempts to recover PowerPoint files automatically in the event of data loss. So you'd better make sure you have turned on the feature. And the next time, when you close the powerpoint file by accident without saved, it also allows you to recover them.