lay on the floor and look behind the sink bottom and you will see a spring clip on a small rod. Squeeze this clip and slide it off of the small rod that it is attached to. Now with a pair of pliers, gently loosen the plastic nut which is holding the small rod in and remove the rod. Chances are that you will find that your sink stopper is clogged with muck. Wipe everything clean and replace everything exactly the way you removed them. Remember not to run any water in the sink while you have the rod out or you will be wiping up water under the sink.