This is one of the most important, yet also one of the most neglected areas of computing. Backing up your data should be at the top of your computer maintenance list, right next to Virus Protection. Without data backup or virus protection, you are running the risk of losing your data. And it will happen, don't think that you don't have to worry about it.
Data loss can happen in many ways.
One of the most common causes is physical failure of the media the data is stored on. You probably have everything saved on your PCs hard drive. That hard drive will not live forever. Yes, normally hard drives will live for years without incident. But eventually they will die.