Finally I solved the problem. While I was removing the PSU #1 to replace it again by the PSU #2 I noticed that the fan of the PSU (which I had changed) was not plugged where it should be. It was directly connected to a MOLEX connector instead to be connected to the motherboard, so it was my fault after all. I still try to understand what I was thinking on when I mounted the PSU the first time to plug it like that.