Who knows? maybe you burned something out when (and if) you connected
the cable wrong. This has been known to happen. Video card sends
signal, signal goes to wrong place do to improperly attached wire and
(depending on content, say it was a +12V trigger for the monitor) went
to the MPU (Microproc unit) or other chip or component and cooked it.
Could also be a solder joint that is cold.