CM1200 problem. Unable to get two devices connected

> CM1200 problem. [...]

   History?  New installation, or did the CM1200 replace some other
device(s), or what?

> [...] Any suggestions other than the brand new router is defective and
> needs to be replaced.

   A CMxxxx is a _modem_, not a modem+router.  If all you have is the
CM1200, then you don't have a router.  And, with typical residential ISP
service, for multiple devices, you need a (NAT) router.

   A quick web or forum search for your model number should find
abundant reports like yours, from folks who (thanks to potentially
misleading claims) misapprehended the utility of the multiple LAN ports
on the CM1200.

   Visit http://netgear.com/support , put in your model number,
and look for Documentation.  Get the User Manual.  Read.  Look for "LAN
port".  Do you see anything which suggests any use of ports 3 or 4, or
any use of port 2 other than for port aggregation?

Just curious, for two devices, are you using LAN ports #1 and #2? 

Is LAG enabled on the modem? 

Power OFF the modem for 1 minute, connect the two devices to ports 1 and 2. Then power ON the modem and let is sync. Does this work by chance? 

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artgreen1 wrote:

I have a HP Pavillion All-in One 24inch desktop connected to internet by ethernet. My brother has a Macbook pro and is connected to the internet with ethernet. we are both using the same CM1200. I have internet access but for some reason my brother cannot connect. My service provider (comcast) could not resolve the issue and said I need to contact netgear. Netgear support was unable to determine what the problem was. Any suggestions other than the brand new router is defective and needs to be replaced. 

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