The 'Computer Idle' rule doesn't seem to work for me. I don't know if there is some device plugged into the PC generating inputs so it is resetting the counter, or if it just doesn't work. I see the 'no longer idle' event go off when I make a new rule containing that trigger, but the idle event never works.
I will write a small guide for that feature today or tomorrow, where you can compare with your configuration. You need two separate User defined rules for this. One of the triggers in each.