You can access modem interface on direct connection without router because some of the router will not allow modem IP to access. Please follow the steps mention on the below article to access interface on direct connection.

http://arris.force.com/consumers/articles/General_FAQs/SB8200-Web-Manager-Access

The direct connection does not work unless you remove the coax during IP address connection to the modem

If you are unable to access the GUI web portal with co-axial cable connection, I advise you to get in touch with your internet service provider and ask them to inspect the cable connection to make sure there isn't any damage.

I had the exact same problem.   My new 8200 would not respond at 192.168.100.1.  I think I did a factory reset and then was eventually able to connect.   I got stubborn with it.

Not sure why moderator suggested checking coax cable while attempting a direct ethernet connection.  

My 8200 eventually responded but the interface of my 8200 is very very flaky.   I get an ascii text page displayed … then its immediately replaced by the GUI page.   I have to login for every page I switch between on the GUI.   And now it refuses to show the event log.   Hmmmm

If you are unable to locate the event log on GUI web portal, I suggest you to contact internet service provider for further assistance.

Thanks but … Optimum techs automatically reply … if signal levels look good then its the modem.   I encounter finger pointing.   IP <->  Modem manufacturer.  Customer stuck in the middle.   For example, my ranging response problems restulted in T4 timeouts with good signal strength and SNR.   My IP claimed it was the modem … after trying 3 different modems.

Event logs are managed only by internet service provider. 

Since you are experiencing with intermittent internet connection, I suggest you to check the cable signals to make sure all the signals are in range.

To check the cable signals, Follow the steps on the below given link:

http://arris.force.com/consumers/articles/General_FAQs/SB8200-Cable-Signal-Levels

If all the signals are in range, then I suggest you to visit www.arris.com/consumersupport for further assistance.

are t4 time outs when it looks like you have a connection but can not connect to the internet?

bought the sb8200 when i updated to 940/35 service, at least every other teams call, the internet drops - but all the lights on my modem indicate that im connected. and my router wont get an ip address. this has happened with more than 1 router.

optimum blames me for having my own equipment and arris wants me to connect a computer directly to the modem which both makes working from home impossible and wont tell me if the internet drops because ill be working somewhere else not using the internet

So, if the upstream power levels are low 42-43 dBmV … instead of 45-61 … then does this mean I need to amplify the signals?   Or does this mean my modem is bad?   Or maybe the head is telling my modem to drive at that level?   Honestly, no idea if I can amplify the upstream channels at all.  

BTW … Just bought a cheap coax tester.   Plan on replacing coax connectors and testing cable runs inside the house.

If the cable signals are not in range, I suggest to contact internet service provider to adjust the signals within a range.

Also, let us know if the problem persists after replacing the co-axial cable.

will do.