Try opening a new blank document alongside the troublesome one. Then copy the content of your original document across to the new one and see if it can be saved normally.
^^^ Oops! I'd not seen Jim's answer. (I'd been away from my computer for a while and omitted to refresh the page). At least we're 'singing from the same hymn sheet', anyway though!
Where did you get the pictures from? Are they on your laptop's local storage, or are they via hyperlinks? If the latter, it could be that they are no longer available for download.
It might also be worth checking that all of your downloaded files are in the same directory and then trying to save the PowerPoint presentation to the same directory.