Most electronic failures occur at time of startup. Your chips and boards are cold, room temperature, and you suddenly heat them up with electric current. If any of the components are weak, this is the time that they will fail.
You don't need a firewall to protect you when you are not at home and your computer is on, just hang up the phone line. If you are still concerned, disconnect the phone line from your modem.
*snickering, shaking my head*..This is a funny thread..