Re: This kind of semi-random, intermittent error is such a pain to diagnose
To add to the stories: in the early '90s I had a call out to one site where the computer was repeatedly reported as crashing. I visited the site to investigate, opened up the computer case, probed everything, sat there for 30 minutes with no problem, put everything back together, still works, left the site.
I got called back again... still keeps crashing.
So I asked the user to demonstrate, while I just sat in the corner and watched and the user did some intensive large-screen graphics editing stuff... after about 15 minutes, yes it started crashing.
I lifted the monitor off the case to open it up.... lifted the monitor.... the monitor..... yes, you know what's happening. The weight of the monitor was just enough to flex the top of the case, and after a dozen or so minute of operation the computer innards had warmed up enough to expand an internal vertical card juuuust enough to touch the inside of the case and cause it to mis-seat in the socket. I can't remember after all this time, but I think the fix was a telephone directory to spread the weight.