Nighthawk C7800 power cycling on roughly 2 minute intervals

AC3200 Nighthawk C7800 - other data unknown (such as firmware)

Recently moved, went several months without internet, now at a place with a COX box not more than ten yards from where I want to put my modem/router.  When I initially connected everything seemed fine, we have Wi-Fi but no internet. Called up COX and got the account activated and they started remotely messing with the modem.

Then they said they would have to send out a technician (at $100), to finish set up. Never had them have to do that before.  Now when I try to get into the modem and router configurations using the 192.168.0.1, I was getting disconnected before I could do anything.  Thought it was because their end was still sending reset commands, so I unplugged the cable.  Initially I made some progress, but then it started cycling power even after I disconnected it from the cable.

I double checked nothing was incidentally pressing the reset button, and that seems clear. 

Sadly, I'm just outside the 1 year manufacturers warranty, but this is the first time I bought a modem and it hasn't worked flawlessly for several years.

Any ideas on how to get it to stop power cycling?