In the New York Times today, there's an interesting article about a computer problem for PCs that has happened to me several times. I'll be getting set up in an airplane to watch a movie or presentation on my laptop when the sound stops working. Once, it was because I downloaded something that altered my sound codecs. Another time, an overambitious virus sweep took out an important driver.
The Times article links to a Microsoft page where you can buy several different codec packages to for about $15 restore your sound (and several other functionalities). The writer then states, "there are several sites offering free codec downloads that can be found with a quick Web search." That's not exactly true. (After all, if it were, why didn't he just link to them?) But, if you're willing to sift through a bunch of links--or finish reading this post--there is a place to find a free download package that has cleared up almost all of the problems I've had: Free-Codecs.com. For my most recent problem, I downloaded an XP Codec Pack that quickly turned my cantankerous DVD player into a useful drive once more.