I've had a PC crash and its not pretty when it happens. Some companies claim they can retrieve your files but my designs came back looking like someone made them into a jigsaw puzzle. Useless to me. I now keep all my files on another hard drive and then back them up weekly. Just the other day I got the "black screen of death" and had to take my tower in to have them fix it. I now know what to do when I goof up the next time though. I had to use my laptop but couldn't get to my files as it was on the extra hard drive in the tower so I'm thinking of adding another external hard drive so I can switch it out between PCs.
And yes, external hard drives can crash too so that's the reason for a backup. There are companies out on the web that provide a backup service for a nominal yearly fee. Some folks like them as it alleviates the worry of losing your files. You can also copy them onto CD/DVD but that's time consuming and if you're like me, you'd have to make new copies all the time.