Cable is good, DHCP server is working fine, switch and port that it's plugged into is good. I've tried connecting it to both the LAN and Internet ports and NEITHER shows a link or any activity. Left it all connected up and powered up for close to an hour, continually rebooting every few minutes - no joy.
Plug in a phone to each of the phone ports with the same results - no dial tone, no anything. Dial ***8, nothing. Dial ***1, nothing. Absolutely no response at all.
I did the factory reset procedure no less than ten times. Every time it went through the light pattern as it should, landed on solid red (rebooting), then went into the reboot loop.
I suspect it's toast.