I have never seen a PC burn up, but my first PC back in '97 had a very low quality 12x CD-ROM in it. It forgot one time to spin down the CD before opening the tray. The CD flew out of the drive, went right by my head like a frisbee from hell and hit the wall on the other side of the room, making a nice little hole in it.
I also had a few LEDs explode years ago in an electronics lab in school when I forgot to put in current limiting resistors. Sounded kind of like a series of firecrackers and the smell was quite bad. No fire but black soot all over the thing.
