black magic = B = Black Thursday

Black Screen of Death n.

[prob. related to the Floating Head of Death in a famous "Far Side" cartoon.] A failure mode of Microsloth Windows. On an attempt to launch a DOS box, a networked Windows system not uncommonly blanks the screen and locks up the PC so hard that it requires a cold boot to recover. This unhappy phenomenon is known as The Black Screen of Death. See also Blue Screen of Death, which has become rather more common.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.