Is it possible that your site was down for a while last night? If so, it could be that th AdSense crawler was unable to visit it, and so couldn't decide what ads to serve. If that's the case, it should rectify itself in a day or so.
Or, do you know any other reason that the crawler couldn't get access? Did you add any of the relevant pages to your robots.txt file, for example?
Finally, you asked how to contact the AdSense team. You can't. The best you can is to use the AdSense Troubleshooter to try to figure out the reason.