Sorry for my late reply... to be honest, I put the MacBook away because I was tired of it.
I hope you are still reading this or get a notification that I'm replying you now.
Just took the MacBook out of the closet because of boredom and did what you were writing:
>> When cleaning, you need to remove everything including RAM sticks, fans, heat sink... anything detachable from the main board. Drying thoroughly is also necessary.
>> Then you connect one fan, the small MagSafe board (where the charger attaches), and you plug in the charger. Must be original charger, 60W ok in your case. In case of doubt, use an 85W adapter. So plug in the charger while making sure the pins are properly aligned otherwise you can fry your onewire circuit. After you plug in, you should see a green light and the fan spin.
Did that... the charger turned green, but no fan spin.
>> Unplug power, attach battery, repeat. If now you have green then orange light, the board is basically starting and charging.
Did that, too... the charger is green at first, but then switches to orange.
>> Again, disconnect battery and power, put board back in the case, and attach keyboard, then battery then power (ALWAYS disconnect power charger and battery between tests). Next attach the screen, also disconnect power and battery until you have it plugged in. If the green and orange lights don't turn on after you plug a certain component, you can assume it is causing a short and preventing the laptop from restarting. Report back.
Done... I attached each component one after another and observed what the charger light is doing. Each time it changes from firstly green to orange.
I then tried to switch it on. You can hear that the hard drive starts to spin, but no screen activity.
Afterwards, I tried to reset the SMC (Shift, Ctrl + Alt) and the battery light changes from orange to green, and after a few seconds back to orange. So the reset works, and the MacBook tries to start, but:
a) HDD spins
b) Fans don't spin
c) No display activity...
I'm afraid I don't know anymore what to do now...