Mine wouldn't start in the cold either. Had to hold the stupid key in for fifteen minutes or more before the fuel line would unfreeze (took me a while to figure out that was the problem). Turned out to be two problems actually: 1) really dirty fuel tank and 2) the diesel was gelling up.
For 1) I unscrewed the fuel tank drain and got the last of the gas out. There was plenty of water in it that I could tell was freezing in the fuel filter/separator. And I washed all the black gunk out too with the garden hose. The black gunk was freezing with the water.
For 2) I hear there are additives to mix in. I haven't tackled that yet.