Netgear C3000 - all channels are locked and cable is inaccessible

I just got a new internet service connection with Cox at my new home.  I bought this modem-router two years ago for my girlfriend, who had Cox at the time.  Other than going down more frequently than we liked, it worked more or less fine.  The Cox tech cam eover last Saturday and hooked everything up and all was working fine all day Saturday and Sunday, until last night..

Around 11:30pm, the wifi went out.  We rebooted the modem-router several times, and all I could find out was that, on the Cable Connection screen, all the cable channels in the modem-router are showing as locked.  Cox does not troubleshoot equipment that isn't theirs, and their Arris modem is working fine (we can use its wired connection for one computer, but that doesn't give us the wifi we need for the phones or other computers).

How do I unlock the channels?  Also, how did they get locked (so I can hopefully prevent this from recurring)?

Thanks.