Used to be that some laptops had weaker USB ports. Might check the supply voltage to the board to make sure they are getting enough voltage?
9v battery as in the small rectangle style? That wouldn't be doing you any favors.
You can dispense with the battery by using the mains to supply the voltage to the gate through a series resistor and capacitor.
don't use pin 13.use another pin like pin 2.. if the voltage is low to begin with, the led will only lower the current further to the transistor.