AdWords also by default shows the last request you asked for. If you asked for a specific date, like Dec. 23, it will keep showing that until you request something different. Try setting it on "today" or "yesterday" and you should see current results.
Also check to make sure that you didn't accidently "pause" your campaign or that you haven't been stopped by Google for some reason.
It has also happened that someone accidently deleted the ad so there is nothing to show.
One of these things should solve your problem.
