If it is hot water, you might have air bubblles keeping the water from getting int othe radiator. see if you can find a radiator key or wrench to open the vents (valves at the end of the radiator) and let the air out until the water starts to come out. Carefull you don't get your hand in the way of the water or the steam! Best let a person do it who has done it before. I do it all the time here, but we have lower temperature in our radiators than the radiaotrs tend to have in the states.