The fans are spinning. The led in the motherboard lights in green. And in the front case, when turning the PC on, one of the 2 leds lights, then off during a second, and then blinks.
I couldn't replace any component (apart from exchanging the memory banks). I've seen that the PSU fan is not spinning but I guess that's normal until it gets some temperature level (but I'm not sure). Do you think that the problem is in PSU? Even if the fans are spinning?