Could be the cooler bottle frozen. in the back of fridge, the cooler bottle. But 1st listen when you press the lever, you can sometimes hear the valve open, If you can, Bottle frozen, even if you cannot, probably same, Some times, just holding the pipes to the bottle at the connection, will be enough to get it running again, The heat from your hands, Or very carefully with a hair dryer, BUT do not put the hair dryer within the unit, just in case of drops of water, Keep outside unit, Also will not damage plastic at that distance but enough to clear the blockage. Mine used to do it, I put some extra lagging over the ends, been fine for ages now
SD, July 2012