TeamViewer is an internet based product, and sometimes there are outages. We understand this and have created a page to allow you stay up to date with us and our availability. You can see at this page if we are having service interruptions or if there is something larger going on.
Please visit status.teamviewer.com to stay up to date or to see if you're not the only one having an issue.
Also you can subscribe to the status page as an RSS feed or Atom Feed.