I don't have too much experience in bonsai altogether, only 5 years worth of knowledge. One of the things i've learned in that time though, is that ponderosa are cold hardy to the extremes. Just as hardy as RMJ, if not, more cold hardy.
I leave my ponderosas on their benches throughout the entire winter, never moving them once. It got cold this winter, to -15 degrees a few nights, not including the wind chill. The ponderosa were sitting frozen to their benches, blasted by the icy wind as usual, and they grew fine this year. I'm amazed by them, i can't believe it when they sprout in the spring. Every winter there are nights where i say "my trees are dead, every one is gone, it's just too cold." But in the spring, they grow. Every time.
Im sorry, i don't have enough experience to find your problem from the short description, but the cold is definitely not what caused it. I'd say just give it lots of sun/water and wait it out.
Unless it's a root issue, I've found ponderosa to be almost bullet-proof. Just give it time...