Registrar and DNS

if your site is already in use, and you want to avoid downtime, the first thing you should do is set up your zone with linode - add all the records you want and (after waiting 15 minutes) check they work with 'dig'. perhaps your registrar won't let you delegate your zone to nameservers that haven't had this done yet.

Did you try it once more from a different network? Looks to me like its a DNS/internet connectivity problem.

If you've only set the authoritative nameservers to us (and not created a domain in the DNS Manager to match), this is what will happen. Complete the guide, and it should be fine.