Dell Precision M6800 Laptop on-board Keyboard not recognized when connected

One of the major ingredients in nearly all sugary drinks is acid of one kind or another.  Acid gives the drink its tartness; without acid, the beverage is rather uninteresting.  In Coke it's phosphoric acid, which is the same acid used to remove rust from steel in naval jelly.  In other drinks both carbonated and uncarbonated -- even Kool-aid -- it's citric acid, which is also an enthusiastic corroder of metal.  Ferric citrate is one of the reasons Irn-Bru is orange.

Chances are you didn't pull the motherboard and flush it with water and baking soda, then soak it in distilled water, then flush it again with distilled water.  If that is the situation, then the acid has been hiding inside and underneath connectors and sockets, slowly eating away at the traces and pins.  At this point it's past repair and a new motherboard is required.

In this situation I'd replace the whole unit rather than trying to replace the motherboard.

You might be able to claim this episode under your homeowner's policy, depending on what kind of coverage you have and what the deductible is.  I see M6800s are going for $250 to $300 on the fleabay, so if your deductible is more than $250 you'll be out of pocket for the replacement.

Thank Klan.
So far, that is the only issue I am having.
I am taking the system apart here in a little while, and I will take another look at it.
As for the water bath, as you mentioned.
I never heard of doing that to a motherboard. Had I known, I would have done that to it.

if only some of the keys worked on the old keyboard, and then when you installed the new keyboard and none of the keys work and you installed the old keyboard back in and none of the keys work, it is possible that you may be installing the keyboard cable upside down or maybe it is not inserted fully into the socket before closing the latch for the connector. This ia a common mistake when people are not very observant when they disconnect the keyboard cable from the motherboard. 

Just adding to the above post.

... or inserted at a slight angle.  Doing that can cause the cable to be not inserted fully but it does seem to be fully inserted.  A slight cautious wiggle can sometimes free a ribbon cable that appears to be jammed and let it go further in.  Also many times there isn't enough room to be able to see, feel, and do the connection correctly.

I hate ribbon cables and ZIF connectors.

I neglected to add two things:

1) Remove the fan before washing.

b) "and then hold at 120F for 8 hours or in a desiccant chamber for 24 hours."  This gets water out that was hiding under components and inside sockets.  Higher temperatures or longer times can cook the water out of the electrolytic capacitors.  Personally I'm a fan of a desiccant chamber as no elevated temperatures are needed, silica gel can be reactivated in an oven, and after a few years collecting little bags labeled "DO NOT EAT" I've got a great big jar of it ready to use.

Welp, I don't have one of the chambers to do that with, Klahn

@Robert
Trust me.
I changed it back and forth several times, thinking that it might be wrong.
And still nothing.

I just ordered a used board on eBay, for $47.00
However, when I take this system apart, I'm gonna take a look at everything to see if MAYBE, there is something a miss.
(I also need to clean the power button, as it sticks a little.

Update

I got the replacement board in the other day.
Replaced it and have it in the system right now.
And guess what?
That blasted keyboard DOES NOT WORK.
So.
Was it the original motherboard that was bad?
Was it the keyboard that was bad?
Were they both bad, and now the replacement motherboard is also bad?

And yes, I made sure I turned the ribbon correctly.
Hell, I even turned it backward and tried it, and still nothing.

I am at a complete loss.
Dell's forum.
I created a TA on their forum, and they immediately jumped in and wanted me to create a support ticket which, since this system is years out of warranty, would cost a few hundred dollars.

Wow you were sure dedicated to this project, that really must be frustrating.that everything you tried is not working. I would have given up at the replace the keyboard stage. It is definitely possible that the person who sold you the mobo on eBay got rid of it because of the fried keyboard port on the mobo. Looks like you are stuck with having to use a external keyboard. At least this has given you experirence in assembling the laptop. You should be a professional now. 

@Robert
When I first got the laptop I took it apart to replace the CPU and add more memory.
This was the first time I took the mobo out and replaced it.
Yep, at least now I know how to replace the mobo.

does the second board react exactly the same way as  the first?
in windows or Bios?

I guess that is why Dell was interested in the case, even though the system was out of warranty. Known issue with keyboards malfunctioning.