It's common knowledge to those in 'the industry' that computers are evil.
Case in point: my file server, Thor.
As Sam has noted, it previously had a hard drive die during our Lan Party this past August. Today, it decided destroying data wasn't good enough. It needed to just tease; like, turn on, but not POST.
I have an older Epox KP6-BS motherboard w/ dual P2-266 processors overclocked to 400; this has run stable for years, but I believe the mobo is on its way out. Many times today I had to reset the CMOS every time I made a hardware change. Eventually, I was able to get it back in place and working, but not after removing the removable drive cages (which were causing problems, confirmed by Google). Oh well. Another day.