Depending on what OS you use, some retain older copies of files. XP Pro is one of them, but Vista and 7 may as well. It is worth a shot.
Typically you would right-click on a folder or file in Windows Explorer and look for a tab that says "Previous Versions". If you don't see anything like that then I'm afraid you may be out of luck. If you do see that tab though, you may be able to restore the file(s) or entire project folder.
I generally only make backups of my project when I am releasing an official version, but I do sometimes make a backup before or after big changes. It's a good habit to get in.
I also have software that makes daily backups to a second hard drive of specific folders that I care most about. Programming projects, pictures, financial, stuff like that.
Good luck!