And one more thing: I don't know why do you need USB in this example, but if using USB, remember to change the power selector jumper from 5 to 3.3 volts. And since you need to do this, I think your USB cannot support the current needed for relay. This can cause pc power off too, I'm not shure. So, if possible in a first moment, try all I said using 5v. only, without USB.