OK, we've all done something totally stupid over the course of working with computers.
I remember a time before I had the knowledge I have now - before I'd ever been inside a PC myself. It was time for me to check out what RAM could go into my rig (at the time a K6 200.)
I happily started unscrewing the screws on the back of the desktop case. Little did I know, of the 5 that were there, only one needed unscrewing. I got the fifth, and *clunk* the PSU fell off.
To be fair, it was pretty funny, thinking back to it, but I'm sure you can imagine how I felt at the time!
Come on guys... your stories!