The cold temp will definitely keep the yeast from carbonating the keg, but it's an either/or thing. Either prime with sugar or force carbonate with CO2.
If you mean you put some pressure on the keg and let it sit cold, then added sugar and got no carbonation, your problem is the yeast won't work when it's too cold.
If you mean you had constant pressure on the keg and let it sit cold and it didn't carbonate, then a leak is the most likely suspect as euge said.