I had an even better one. While back, had a Pentium 3 that was rebooting without warning, seemingly at random. My old man is an electronics genius and I was quite handy with computers at the time, and he figured it was a dodgy power supply. We pulled the computer out, pulled the power supply out and apart and had a look at it. All looked good, so we left the computer on the kitchen table and plugged it into the mains with an extension cable, to see if the powerbox was making noises or whatever. It was then that the foot-high flames started coming out of the power box, and it was then that we realised what the funny smell had been the whole time... The old man had to go out for a bit, so he turned everything off and said "Now Pete, don't go playing with this, wait until I get back, and especially don't touch both terminals inside the power box." I neglected the first piece of advice, and ended up neglecting the second, too... Yay for almost dying!