Do not panic, there is a global bug with Google Webmaster Tools where Google is reporting that your site has zero pages indexed. This is currently a confirmed bug impacting all sites in Google Webmaster Tools. Google posted this in the known issues area saying:
The indexed URL counts for Sitemaps that you have submitted in Webmaster Tools may be showing zero (0) indexed URLs for some sites. We are aware of this issue and are looking into it; you do not need to take any action. This will have no effect on your site's performance in search results.
So don't worry - Google will fix it and you do not need to do anything.
There are literally dozens and dozens of threads with complaints. Here are just a few of them.
Update: At about 1pm (EST), I checked back to see if this has been resolved and I am seeing indexed counts at normal levels now.