When making your backups of bitcoin, the wallet.dat file is located in the user file, (actual users name), AppData, Roaming, Bitcoin folder.
Yeah, it's fascinating, the bitcoin client automatically put the wallet.dat very well hidden somewhere in the computer without even telling it to you
And then we wonder why bitcoin is not widespread used?
Many (or most) programs put their data in that area. The idea is that when you do backups you are supposed to backup the whole AppData folder. That way you get all the various data at once and don't have to go searching through places all over the system to get it. It doesn't help much if you don't realize that though.
Another program that may help you find it is TestDisk. But you do need to stop using the disk right away as every disk write potentially is overwriting the sector it could be lingering in.