At last got the relay installed.
here is the relay 40amps a little overkill but everything have his own fuse
here is the outlet that it will be controlling and the line that goes up (the orange one ) that goes to the lights
here is the relay connected the back part cuts the live wire to the outlet and the front one goes to the computer so the 12v line (it accepts from 3 to 32 volts dc)
here is the connector that goes to the computer's power supply
and all installed
i did a power on test and when the computer boots up, the sound and lights turn on with it and when i shutdown everything turns off. I am glad everything worked