There're so many things that can go wrong on a computer. Sooner or later one of them can hit like a bold out of the blue, and you can lose everything on the computer including your email, contacts, photos, documents, even Windows itself. Among the things that can happen are viruses, power problems, software bugs, failing power supplies, hard drives and motherboards, accidental user created problems, etc.
I urge you to get yourself an external hard drive and a good 3rd party backup program. You can set it up to do everything automagically at the time and frequency of your choice. 1 TB external hard drives are about $70 these days and a really good FREE backup program is the Easeus Todo Backup Free which you can download from
http://www.todo-backup.com/products/home/free-backup-software.htm . That can save you a lot of time and frustration the next time something like this happens. Sooner or later it happens to all computers for one reason or another.
why need to back-up?