This is the most traumatic technical difficulty. Unfortunately, crashing (when the computer shuts down by itself) is part of the cost of doing anything on computers. This is because the underlying software that makes them run — what's called the operating system, which is Windows on PCs and Macintosh OS on Macs — can be volatile. But operating systems get more stable every year, and the newest versions, Windows XP ($199) and Mac OS X ($130), crash much less frequently than older versions do. So, depending on how irritated you are, it may be worth upgrading.