Clients not coming back after dns error

Hi All
Last night i checked my server it was running fine ( debian cccam 2.14 ) i tried to connect with putty to the server when i was in work this morning and got a no such server or similar message, very strange i thought and i tried logging in with my no-ip address and could do without a problem, so the problem was with dyndns.
I couldnt login to dyndns to check so had to make a new account, i tried creating my old dyndns name and it worked, the only thing i can think of is the account expired , i cant remember getting a renewal email for it, or do dyndns just close accounts?
Anywho i am using the same dns as before but out of the 23 servers i have only 10 have appeared back as clients, any ideas where its went wrong as people cant seem to connect to me but strange that half of them can???