MacBook not booting up, keyboard?

[throne]

I have a white MacBook from the middle of 2009. This morning when I woke up and went to use it, I noticed that it was turned off. This is abnormal because I generally always leave my computer on and I would remember if I turned it off the night before because it's so out of the ordinary.

So I try turning it on and the computer gets to the Apple logo with a spinning wheel. Shortly after though, it shuts down before it even gets to my desktop. My computer is out of warranty so I decided that since Apple almost always charges an exorbitant amount of money to fix things that are out of warranty, I figure that I'll disassemble part of the laptop and see what's wrong.

Long story short, I disassembled it and took out the keyboard that came with it. I then proceeded to plug in a non functioning keyboard (friend spilled lemonade on it) taken from my friends old MacBook and voila! It worked. This is really weird though since my keyboard that was in otherwise perfect condition didn't work but my friend's keyboard which had been damaged by liquid resulting in some keys not working worked perfectly and allowed it to boot to the desktop. Why is the keyboard even affecting the MacBook's boot up?

So it looks like I'll have to buy a replacement keyboard for my Mac but I think first, I'll stop buy the Apple store to see whats up and if they can possibly replace it for free. This is just a really weird thing that happened considering that I didn't spill anything on it the night before and it randomly decided to stop working.

So here are my questions..

What possibly caused this to happen?
Can Apple tell if i disassembled the computer? As far as I could tell, there weren't any indicators showing that the device had been opened like the iPhone.
What is the likelihood of Apple deciding to fix it for me assuming they don't know that I opened it up?

I typed this all on my iPad so I think I may be forgetting some stuff, it's difficult to scroll up and down in this text box and proofread everything.

 

[i.moroney]

It could be that you have been pressing the keys a little too hard? or there is some small metal piece from your keyboard that is messing with the inside components.

I'm not exactly sure but this is peculiar; try buying a new macbook keyboard and you might be ok

 

[johnnyham]

I've had the power button on an otherwise perfectly fine keyboard go bad before. I ended up wiring my own button, since the Macbook in question was being used as a media center with an external keyboard and mouse. The bad power button seems like the most likely explanation to me. A new keyboard for your model will run you around $30 on eBay.

As for your questions about taking it to Apple, as far as I know there are no tamper indicators on the body, only the optical drive and hard drive. As long as there aren't any bent pieces of metal, missing screws, or scratched up stuff, you should be good. Apple should replace it for free, so long as you have Applecare. If you don't, the cost will probably be more than if you did it yourself. And since you've already done some basic diagnosis with a friend's keyboard, I think you're sufficiently qualified to install a new keyboard