@Saladin said:
Back when I was still in high school I was working in a similar position (a tech at a mom & pop computer shop, a three-man operation including me). One day (this was when 1GHz processors were the brand new thing on the block), we got our first order for a 1GHz Athlon machine for a customer build, so we started work on it one afternoon. After getting the CPU and motherboard seated, it was closing time so we left it there and went home. The next morning, the boss was in to do some paperwork (he usually just came in for that; me and the other guy pretty much ran the place), and he says "Oh, cool! A gigahertz processor? I gotta see how fast this goes!" and fires up the machine, despite there being no CPU fan or heatsink on the processor. Exactly six seconds later, a small popping noise can be heard (like a piece of bubble wrap being stepped on) and a little spiral of smoke wafts up from the (then quite expensive) processor.
How's this: I was working on the first computer I ever owned (~1999ish). In order to get access to some drives I took the heatsink off. While rotating the case I managed to jiggle a USB cable which was plugged in. At this point I learned three things.
1) Never work on a computer with the power cable plugged in
2) A USB device can boot a system
3) Never do either of the above with your thumb on the processor core
Yeah, it hurt.