If you're tired of leaving your PC on continuously so that other machines in your house can access the files you store on it, you're ready to step up to network-attached storage. As you might guess from the name, NAS devices connect via ethernet directly to your router.
Your network storage device can be a stand-alone unit designed specifically for centralized storage, or you can convert an old PC into a file-sharing device. Either way, you'll have a 24/7 data repository for backups and for sharing documents, images, videos, and other files.
A NAS device should be isolated in a safe, cool, dry, out-of-the-way place to make it less vulnerable to bumps, spills, and other physical dangers. (Plus, hiding your storage device keeps it safer from theft.) Though off site is the safest destination for your backups, NAS can be the next best thing--barring tornadoes, tsunamis, and other acts of nature.
NAS boxes are isolated from most of the software dangers that networked PCs fall prey to, as well: Even if the files stored on a NAS device get infected, the box's operating system resides in its firmware (unless you're using a retasked PC), and is therefore very difficult to attack.