I'm not sure how much of a hint this is but given the fact that some people might run into this serious problem and then start looking for solutions on macosxhints, makes it worth submitting.
Some time ago, right after upgrading to 10.2 (after a reformat), my PowerBook started acting up; the computer would all of a sudden freeze up in the middle of whatever i was doing. I naturally ran all of the required software tests such as Norton, Techtool, fsck and so on and they always seemed to find problems, but after having these apps'fix them, my PowerBook would still freeze up.
After a while, the problem got worse. After force-quitting my PowerBook, it wouldn't boot anymore; instead of the well-known sound, it would give me between three and four ring tones. After some research on Apple's support site, it appeared that these ring tones indicated a RAM problem. Strangely enough, the Apple hardware test CD did NOT find any problems.
Read the rest of the article for futher diagnosis and the eventual hardware-related fix...
I then decided to bring my PowerBook to My Apple Service Center where they performed several extended hardware and memory tests ... BUT didn't find any problems whatsoever. Nevertheless, since I'm a good customer there, I convinced them to put in two new RAM sticks. Coming home and reinstalling all my software and data, it took no longer than 30 minutes for my PowerBook to freeze up again. You'll believe me when I say that I was about to break down. I ran all of the tests again and again, but the computer kept freezing. Of course I thought about having it send off to Apple Europe, but I was afraid that they wouldn't find anything either and just send it back.
After a lot of conversations and discussions with my Apple service center, they decided to replace the entire logic board since it was clear it was a hardware problem. This whole procedure took about 15 minutes and my PowerBook has been running without a problem or glitch ever since, which is almost a month ago.
So, if someone stumbles upon this hint and recognizes the symptoms, just get the logic board replaced. Trust me, I was working around this problem trying to find a solution for a couple of weeks. The silly thing is that I still don't know what went wrong exactly with the logic board, my Apple Center didn't either, but Apple was 'kind' enough to give me a new logic board for free so I suspect it must be an issue they're aware of.
[Editor's note: Although this isn't directly an OS X hint, there are quite a few troubleshooting articles here, and I thought this might be useful to have in the archives just in case someone else runs into the same thing.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2002122006002188