Macbook 13" and a new logic board

Hi. I have a Mackbook 13" with a faulty logic board. I've bought a new logic board and replaced my old logic board with this new one, but when I press the power button, nothing happens. The led of the charger lights in green. So I decided to disconnect the blue battery of the logic board, to wait some time and then to connect it again. This time the computer turns on as soon as I connect the charger to it. However the macbook goes to sleep every five seconds. The LCD light goes off. And when I turn the computer off, I can't turn it on again whithout reconnecting that little battery of the logic board. It seems like SMC reset is needed, but that 5 second way doesn't work. Can anybody help me, please?