If your hard drive is seriously f*cked, and you have some big shiny balls (or you're dumb as hell), you might be interested in how a fellow from Mandible Games claims that he recovered data from his drive. According to the article, he noticed that his drive would spin, but it would not show up in BIOS and there was a distinct and repetitive clicking noise.
After a little experimentation, he realized that it the heads may have gotten misaligned or stuck, and if he could jar the heads loose, it might work again. Naturally, when you heat something up, it expands —so, in theory, if the drive was heated, it should have the same effect. Apparently, by double boiling your drive you can achieve the proper amount of heat without doing any further damage —and the guy claims that the drive worked perfectly after the procedure.
Would I do this? Hell no—but then again I'm not a lunatic and I'm not willing to screw around with important data. However, if your idea of troubleshooting is to bang on it with a hammer, or your are too cheap to pay someone to recover your data, this may be something to try. [Mandible Games via Spluch]