Does your web browser (for example, Firefox or Chromium) show an error message indicating that it can't find your site? Are you also unable to send and receive emails? SOS!
In almost all such cases, the problem is that your domain name (example.com) has not been renewed. If you act fast, you will probably just need to pay the annual fee in order to re-activate it. This fee is paid to the domain name registrar, not to Koumbit. The most common registrars are Tucows and Godaddy.
Domain name registrations are public information (including who registered what name, and from what regisrar). This information can be found through a "who is search", which can be done through various websites. If you have trouble finding which company is your registrar, you're welcome to ask us. This information can be found quite quickly.