hmm, honestly the biggest disaster I ever had, was: If I can remember right, I was helping a n00b build his first pc. I left the room and figured he could get the cpu and heatsink in properly. I came back, and the pc was done. I told him good job, and to move on to OS installment. Everytime it turned on though, it would run for about 10 seconds, and shutdown. Well, it turns out that he put the heatsink on backwards... the processor overheated, you get the idea (Kentucky Fried Processor)...