There's a saying in computing about hard drive failure - it's not about if it's going to happen, it's about when it's going to happen.
Computer hard drives are intricate pieces of machinery and many things can cause errors or corruption to occur - either on the physical drive itself or in the files on the drive. Bad downloads, files that didn't completely transfer, software or driver updates that don't complete properly and viruses and trojans all can spell disaster for your data.
If your data are important to you (documents, pictures, music, email, addresses - things you've added or created), they need to be protected for the time when a failure happens. Waiting until something happens to try to retrieve and repair or clean your data is time-consuming, expensive, and not always possible.
There are a number of backup solutions, many automated. An external hard drive is probably the safest and easiest way to make copies of things you don't want to lose. You can find fancy backup software to buy that claims to make your backup chores simple. Just be aware you don't have to and probably shouldn't buy anything; external hard drives ususally come with their own software. However, for me, the safest way to save your data is to simply copy it in it's current format to another type of media. Burning cds and dvds is another good, long-term solution. The best backup plan includes both external drives AND burning dvds.
Many people have become satisfied with using USB flash drives to "back up" their important data. While flash drives are a good way to transfer data from one computer to another, they cannot be considered safe or long-term storage. Although many flash drives have survived repeated trips through the washer and dryer, many others (my own included) have simply failed to read the data just copied to them for a multitude of reasons. Consider them convenient and temporary.
If you have questions or want help implementing a regular back up plan, send me an email and we'll put something together. Somewhere down the road we'll both be glad you made the effort.