Power Point presentation is suddenly gone. How can I restore it?

I have to prepare a presentation for the school via Power Point. I use Open Office Impress from Open Office. I had finished the entire presentation and saved it again and again, I only changed one slide a little bit but saved it again before, when my laptop had hung up. I had to shut it down and restart. When I started it again and wanted to reopen the program, all the documents were gone. Everything I had written months before and the power point was gone too. How can that be? It comes then permanently: No documents available.

How do I get the things back? It would be really important otherwise I have to do everything again. Why are the things gone at all?

Would be very grateful for answers.

It's hard to say from a distance, that can have many reasons. Have you ever tried to save a file in the directory where your Powerpoint presentations are located?

No I did not. But that means the PowerPoint is gone, right?

No, not necessarily. First try to save something there. What is happening?

There appears only the file which I saved now nothing else is there…

Why is PowerPoint gone if you work with a completely different program "Impress" and also save files with it?