Power Bar stopping gameplay?

I have a power bar that runs out when clicking spacebar to many times. How do i make it so that once it reaches the interval 0 it will disable the spacebar from working and thus making the actor fall to the ground? Keep in mind i am very new to gamesalad

Comments
At the moment you must have something like this :
Rule : Key Space is down ... then .... do this (e.g. make guy fly)
You need to add this :
Rule : Key Space is down AND game.power > 0 ... then .... do this (e.g. make guy fly)
So it checks whatever game attribute you're using to for the power level and if its zero it will break the rule. I assume you wait a few seconds and power climbs back up? At which point he can fly again.