is it indoors or out? If it is indoors then it may be suffering from dry air if you have central heating. Try positioning in a slightly more humid place - or put on a tray of damp pebbles. But it won't want too much humidity either so keep an eye on it.
If outdoor it could be a victim of the cold, damp winter. Tho' we have a ten year old one outside that has experienced -10 a few times. I would cut off a small twig to see if it is still green - or just give it time and see if new shoots start with the warmer weather.