Stopping a Defrag in mid-stride is like a sky diver changing his mind after he's already jumped out of the plane. Not a good thing!
I'll go along with "Miles Ahead" on doing backups at regular intervals, like weekly.
First and most important, is that your Backup & Restore program is not solely on your HD. It becomes 100% worthless when that drive crashes.
So, you need a backup/restore program that can reside on either a CD or Flash Drive. Then it must be able to backup your entire C: drive and store that as an Image File to some other drive or media..... so when disaster strikes, doing a Restore can put your C: drive right back the way it was the moment you made the last backup.
I use an older backup program called simply "Ghost" that I run from a Bootable Flash Drive or CD and it can not only make a backup image file and save it anywhere I designate, it can also compress that backup image file, and check it for accuracy, so I can store many of them on my 1TB storage drive. I have has HD crashes like anyone else, but I've never lost any data,* because of my weekly backup regimen.
*My data files (My Documents) are backed up daily, to a 128GB USB 3.0 Flash Drive. It takes only seconds.
Good luck, on sorting out that messed up HD, without a backup image file to restore. I think in that case, I'd save all the data files I could find, to an external HD or Flash Drive, and reinstall Windows.
Happy Holidays!
TechnoMage