Did you register, and configure the domain at http://co.cc ?
co.cc domains are provided by a third party, the do provide most of them for free. We recommend configuring it to use our name servers which are: ns1.x10hosting.com and ns2.x10hosting.com
That's odd, I don't know what changed it. I'm unable to change it again because my domain isn't listed under my account(for some reason) at co.cc. I think I'll contact their support team.