This happen when your domain has expired and you haven't renewed it.
When a domain expires the registry point the domain to a placeholder page while they give you the grace period (usually 15 days) to renew your domain registration. Also note any service you have in the domain such as email services, etc. will stop working if the domain expires.
To avoid this happen renew your domain at least one day before the domain registration expiry date.
Once you renew your domain they will point back the domain to the original nameservers, keep in mind the propagation time until you can see your site again and you services start working as normal can take up to 24-72hrs.
