yeah you read that title right. can you believe it? I fought with my computer for an hour early this morning, installed a super fresh kernel, played with intel drivers, but nothing wanted to make ubuntu 14 recognize the displayport. It was working the night before!
finally gave up and went to put some music on. boom! screen turned on. what the hell? unplugged the eighth inch cable again. boom! screen turned off. also, the amplifier turned off and on each time I plugged or unplugged the cable. I'm still 99% baffled here but there's another clue - a buzz on the line that I can audibly hear thru the speakers when this particular sound system is connected, that also changes when I restart the computer.
Note that when I plugged headphones into the eighth inch jack, the screen did not turn on (altho there may have been some signs of life briefly).
So best guess (which is probably very wrong?) is that there's a loose connection somewhere in the laptop, and that the added power from my stereo thru the eighth inch connection (which should be flowing the other direction, but this is an input / output jack) is bridging the loose wire? hence the buzz?
UPDATE 6:30pm same night:
scratch the above theory - new shit has come to light!
when I moved my laptop to the living room and plugged the mini displayport into the projector, everything worked as always - without a sound system being plugged in. So then, being the good scientist that I am, I lugged one of my screens into the living room and plugged it into the displayport, and holy moly, it worked fine, no audio cord plugged in. So it's actually proximity to my crazy stereo system that's causing this issue. Unfortunately I don't know enough about sound systems and electronics to posit a complete theory, altho I bet this is enough for someone to be able to. My general idea now is that the magnetic field cast by the bass amplifier on the floor right next to the monitor is somehow involved.
As before, if you have any ideas, I'd love to hear em.
facepalms: 7.5 (would have been 10 but tempered by the sweet relief of seeing that screen turn on)