At the beige box retailer I worked for, about a decade ago, we got a couple of the local high school's computers in for repairs. They told us the systems just wouldn't boot, and they "smelled funny."

Took the case off, and behold! The Intel fan had seized, melted, and caught fire. It wasn't a particularly old system so I'm not sure how the thermal protection didn't kick in, but that had happened on two near-identical systems. No saving those boards.