I had a friend complaining that his new computer I built for him was crashing a lot.
So I go there and spend a good bit of time trying to make it crash. Nothing.
Then his girlfriend gets bored and picked up the wireless phone. Bam ! Computer crashed!
It had to happen another time for me to realize it crashed when she was picking up the wireless phone. Turns out the phone base was on top of the computer. Tha cpu was a AMD 950MHz and the phone a 900MHz phone. I have no ideas if the frequency is at fault or the phone base was creating bad interferences somehow but taking the phone base away from the computer finally solved the problem.