Had the same problem with my 9000, guessing the 8000 is very similar, there is a couple of wiring harness's that gets unplugged when you do key work on these boards, One (mic) has a tendency to get itself under the works and looks like its been plugged in when its not. With the board upside down on a work bench(table) setting on a layer of foam rubber (a must) keys next to you, remove all screws necessary and take off the back. look a little to the right of center on the inside closest to you, for wires that are plugged in, should be two sets, these wires will sort of memorise where they lay. one is probably unplugged seems like its the (right) one. if its not apparent give a little tug on them and see if one is hiding. Plug it in and put it back together like all the other guys suggested. They got it right, only thing I could add is if you have to disassemble don't unplug anything that can be layed back and held out of the way with masking tape. For unplugging wiring harness'es I use a awl or icepick (I also use magnifier glasses to do this) The most I repeat the most important thing is to not let any screws fall into the works, they can get lost and hung up in there and can take hours to retrieve and must be accounted for or can short out your board if left in. I take screws out and lay them in piles in the reverse that they go back in, Garys masking tape is a great tip,for the case, make sure the tapes on tight, cause you probably need to turn the back over and give it a good cleaning and blow out with air if you have a compressor.
You can use a battery powered phillips screwdrive to remove the screws, but put them back by hand preferrably using a magnetic tip #2 phillips.......Pose

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