CM1150V Will not work with Router only Ethernet connections

[RonTWN]

I pourchased the CM1150V to replace me rented cable modem with Xfinity.  When I called Xfinity I was able to get the modem connected to Xfinity and the telephone lines working, however when I plugged in two different Netgear nighthawk routers, I was unable to get an interent connection either wirelessly or wired.  Xfinity said they everything looked good from their end and there was nothing they could do.  I tried another brand cable modem with the same results, so I believe that the issue is with the signal I am receiving from Xfinity.  Has anyone had a similar issue and is there something I can say to the tech to get it working?

[plemans]

you're not connecting more than 1 device at a time to the cm1150v? 

It has multiple ports but can only use 1 through xfinity. Or 2 if you have port aggregation (most routers don't). 

Try powering off both the modem and router and disconnecting everything from each.

then connect coax to modem and power it up. give it several minutes to fully boot.

then connect port 1 on modem to wan port on router.

boot up router and give it a couple minutes. Then try it.