Check if the always create a backup copy was on: Tools>Options>Load/Save>General, Always create a backup copy.
If it is on you should see on that screen where to go look for saved versions. If its not on now would be a good time to turn it on because if you didn't take any kind of backup yourself then your work is probably lost.
Backups are a funny thing, they are such a waste of time up until the point they are needed. I like to use auto save features but for things that are important I always do something to back them up at the very least save them under a different name, backup to USB key, email the file to myself, or sync a copy on cloud storage.