WARNING: This post was originally published in 2008 and hasn't been updated since.
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This has got to be one of the weirder features ever made:Computer Randomly Plays Classical Music
During normal operation or in Safe mode, your computer may play "Fur Elise" or "It's a Small, Small World" seemingly at random. This is an indication sent to the PC speaker from the computer's BIOS that the CPU fan is failing or has failed, or that the power supply voltages have drifted out of tolerance. This is a design feature of a detection circuit and system BIOSes developed by Award/Unicore from 1997 on.
How do you come up with this stuff?!