Thanks! I must read first the datasheet, that would be help me a lot.
I've mounted following the diagram I post in the last post, but it doesn't work. I haven't any photo to upload, in a couple of days I'll make them.
I've realised that the NPN make a noise, but only once when the program begins. Afterwards, the code of a simple delay lights the led and turns it off, but the relay doesn't response more than the first time. And If I connect the outputs of the relay to +5V and gnd from the Arduino, the device begins to shortcircuit and the leds emit dangerously, noising and at the end the Pc switchs off suddenly. bu the Arduino is alive.
I'm sure something is wrong linked, but all of you could help me when I upload the photos.
Thanks!