Thanks for the reply.
I saved the file on the hard drive (C:).
I know the file name.
The timeline was something like this:
Wed morning - worked on presentation, saved file, shut down laptop, no problems.
Wed evening - did lots more work on slides, then saved file, waited for "saved to this PC", I didn't close the file, put laptop to sleep.
Thu morning - woke up laptop, couldn't get it to display on a TV, so closed PowerPoint, extended display, opened PowerPoint, file was the same as the Wed morning version. I then did a full search and found a shortcut file in the "Recents" folder which had
a time stamp that coincided with the time I was editing the file on the Wed evening, but when I opened this link it was the file from earlier that day ... I was just about to go in to a huge Wrap-up meeting, presenting all my findings from a 5 day audit to
Senior Managers - bad timing.
At no point did I change the file name, I know for sure what the file was called. The laptop wasn't connected to the internet at the time, so it wasn't backed up to OneDrive.
This happened to me before, when I lost a huge presentation that I had to do again almost from scratch. Since then I tend to keep saving different versions of files (with different file names), but I forgot to do this last week.
I haven't got the laptop with me at the moment, but I will try to simulate it at some point.