Lost Important File On Microsoft Office?

I have a school report I've been working on for amonths now on my Mum's computer. I recently purchased my own, so I emailed the file from her computer onto mine and downloaded it onto my Office Word 2007. The file was uncompatible with my version of office (even though it was from the same disc we bought for my Mum's computer) so it was always saved to autosave. In order to upload it to the school it needs to be saved to the computer and not in autosave. So I tried to save it, and got a pop-up message that told me it was incompatible but I could still save it with no problems. (i don't remember the exact wording) So I went ahead and hit "yes". now the file is missing from the computer and no matter how much searching I do i can't find it. Any shortcuts or links to it that existed before don't exist anymore.