domain suddenly doesn't resolve

[Gerald Waugh]

I have a server that I tend ns0.hostshq.com
Suddenly nonthing in the hostshq zone resolves
hostshq.com
ns0.hostshq.com
ns1.hostshq.com
Another zone on the same server is acting up
freelance-direct.com

auction-buyer.com=20
centerprice.com and=20
usabidders.com=20
all on the same server work OK

Can anyone tell me what went wrong?
They have been working

Gerald