Why did you save the presentation to PPT instead of ODP? You wanted to open the presentation in MS PowerPoint as well, right? I think this must be the only reason. Can you open the file in OpenOffice.org Impress? When do you find the slides are corrupted, opening the file in MS PowerPoint or OpenOffice.org Impress?
The file is saved in .ppt, so you have one option to repair it by using
Open and Repair of MS PowerPoint. If still the problem persists, you need to take help of a third-party recovery software. Get any ppt repair software and try to recover your file. But before buying the full version I personally suggest you to check the demo version. Demo version of a software is freely available and works exactly similar as full version.
I have also faced such a situation in my past. Not exactly similar to this one, but quite resemble. I had around 30 presentation files of my business project. All went corrupted due to an obscure cause. I tried several things but to no avail. Then I used the demo version of sysinfotools ppt repair, it showed all my slides in the preview session. Though I was not able to save them due to the limitation of demo version. Then I got its full version and saved all my slides. All it took just half an hour.
You may also check this software. Its demo is free. Try it.
