Create a new blank presentation in PowerPoint, and save it under a new name.
Then, go to Format -> Slide Design, choose to show all documents, and choose the corrupt PowerPoint file. Now, go to Insert -> Slides from File, and select the corrupt PowerPoint file. Make sure you are set to insert all slides, and then import. If that works, great! I suspect, however, that you might crash at that point. If so, try repeating the process, inserting specific slides one by one until you find the problem one. After that, save the file, making sure that Fast Saves are off (in Preferences/Save).