Is my computer supposed to do this?

Hi. I plugged in a cable to the "Line In" socket in my desktop PC, and when I started to put the other end into the headphone socket to my laptop, my laptop just switched off, with no "Windows is shutting down" messages or nothing. I never put the cable in fully, but the point of the cable did interact with the outer ring of the headphone socket, causing a strange buzzing noise to come out of the desktop PC, but it always does this, even when I plug my iPod in! I was concerned that this would be a fire/some sort of hazard, and don't want to retry without the OK. -Thank You for you're help in advance!