The below is the most common remedy for leaking clearomizers or clearomizers which are not producing any vapour:
If the battery appears to be working fine (ie if the button lights up as expected when pressed), then it is possible some liquid has gone down the central part of your clearomizer. If you think this could be the case, please try the following: unscrew the clearomizer, place a tissue where the battery was and blow into the mouth piece a couple of times. If there was any e-liquid in the centre pipe this should remove most of it. Now screw it back on and try it again.
Please note: another issue which can cause a connection problem with the battery is the over-tightening of the battery with the clearomizer. If you try the above and it does not work, try loosening the connection between clearomizer and battery slightly.