MacBook extremely slow and strange power button

Hello everybody,

I have a very esteemed macbook late 2011. The logic board had a problem with the detection of the ram memories (3 beeps), which was not repairable so the only solution is the replace of logic board. I managed to get a board of a macbook 2011 early version. I replace the board with very carefully, apparently without any problem and I took the opportunity to change the thermal mass of the processor.

When I try to turn on the computer, I notice that the first strange symptom was that for it to turn on, I had to leave my finger fixed on the power button for about 5 seconds. If I only clicked once, as it should be, I would hear the computer trying to connect but then it would go down. When he finally turn on i notice that is extremely slow, to the point of not being usable. I started in safe mode and it worked at normal speed.

Another thing I noticed, is that I can't reset the SMC. When I do the key combination + power button, the computer wont turn on.

Will these problems all have the same origin or will they be several problems? Do you suggest a solution?

Thank you all!