Check to see if you have a problem with the gasket. If it has cracked or become warped, it could allow water to seep through. Also check to see if there is a problem with the plug on the unit and ensure it is properly plugged into the wall as it should be.
Air conditioning units produce quite a bit of water when they run. A steady drip is average. If that is what you are leaking, you most likely have your tube that drains the water blocked. Run a snake through the tube until your leak stops. Check the exit of the tube to be sure it's draining properly.