Solved! Go to Solution.
Why did you disconnect the modem in the first place?
I unplugged my modem from the coaxial cable for a few hours while setting up a new entertainment setup. I plug it back in and it won't go online.
Triple check the cable. Any chance anything was unhooked at the other end of the cable whereever the wall cable goes? By you or anyone else? You may try resetting the gateway to factory settings by pushing in the little hole in the back with a pen for about 30 seconds. You'll know it worked if eventually all the lights go off and then all light briefly and then it starts to reset. Call in and ask them to provision your modem. Have them check your boot file and rate codes. They will ask for your modem's serial number and CM MAC address. Have them handy on a piece of paper.
If all else fails schedule a tech visit.
Oh, and how long did you let it do that? Your device simply could be downloading firmware. (but unlikely if comcast said they couldn't connect to it.)
Many times I've seen gateways have to go through a 30-60 minute cycle of downloading something before it will then shut off and light up properly (and it lights exactly as you described it). And usually it will light up and reset itself two-four times before it is finally done and stays working and is ready for service.