MacBook won't turn on... logic board seems to be okay.

so I've got a water damaged 13" unibody macbook pro. it doesn't turn on and it doesn't charge with the magsafe adapter. no light, no 'bong' sound. it's not resposive at all with the power button pressed. battery is good.

I thought the logic board was toast but I was able to borrow my friend's macbook pro for shortly (exact same model 2010 13") and did a logic board swap.

first I put my friend's good logic board into my damaged macbook and tried to power it on but it did NOT power on.

next, I put my damaged logic board to my friend's good macbook and tried to power it on and it DID power on!

although the display didn't power on, but the light came on, sound came on, and everything else seemed to be on.

so I came to a conclusion that something other than the logic board on my macbook is preventing it from turning on.

I first thought magsafe could be bad, but both test runs I did were running on fully charged batteries.

Could a bad magsafe board keep it from turning on?

and other might be a bad power button, but could a power button and its cable have gone wrong that easily?

i'm trying to trouble shoot this and get my logic board to work on my macbook but puzzled by the result. i wish i could test some more with my friend's macbook but i could only borrow it for a short period of time...

what could keep it from not turning on?