Assuming it is plugged into a good power source and turned on (no offense intended, just getting the obvious out of the way - and I've fallen victim to the obvious myself before), look inside where you put the paper - is there a trigger mechanism? Most electric staplers have them (the paper hits the trigger and the stapler fires), and some allow you to set the sensitivity of the trigger. If yours allows you to adjust the sensitivity, try adjusting it. If it's not adjustable, the trigger probably needs to be replaced (under heavy use, they may need to be replaced every year or so).